diff --git a/agent/i18n.py b/agent/i18n.py
new file mode 100644
index 0000000000..98d7ebce9a
--- /dev/null
+++ b/agent/i18n.py
@@ -0,0 +1,230 @@
+"""Lightweight internationalization (i18n) for Hermes static user-facing messages.
+
+Scope (thin slice, by design): only the highest-impact static strings shown
+to the user by Hermes itself -- approval prompts, a handful of gateway slash
+command replies, restart-drain notices.  Agent-generated output, log lines,
+error tracebacks, tool outputs, and slash-command descriptions all stay in
+English.
+
+Catalog files live under ``locales/<lang>.yaml`` at the repo root.  Each
+catalog is a flat dict keyed by dotted paths (e.g. ``approval.choose`` or
+``gateway.approval_expired``).  Missing keys fall back to English; if English
+is missing too, the key path itself is returned so a broken catalog never
+crashes the agent.
+
+Usage::
+
+    from agent.i18n import t
+    print(t("approval.choose_long"))                       # current lang
+    print(t("gateway.draining", count=3))                  # {count} formatted
+    print(t("approval.choose_long", lang="zh"))            # explicit override
+
+Language resolution order:
+    1. Explicit ``lang=`` argument passed to :func:`t`
+    2. ``HERMES_LANGUAGE`` environment variable (for tests / quick override)
+    3. ``display.language`` from config.yaml
+    4. ``"en"`` (baseline)
+
+Supported languages: en, zh, ja, de, es.  Unknown values fall back to en.
+"""
+
+from __future__ import annotations
+
+import logging
+import os
+import threading
+from functools import lru_cache
+from pathlib import Path
+from typing import Any
+
+logger = logging.getLogger(__name__)
+
+SUPPORTED_LANGUAGES: tuple[str, ...] = ("en", "zh", "ja", "de", "es")
+DEFAULT_LANGUAGE = "en"
+
+# Accept a few natural aliases so users who type "chinese" / "zh-CN" / "jp"
+# get the right catalog instead of silently falling back to English.
+_LANGUAGE_ALIASES: dict[str, str] = {
+    "english": "en", "en-us": "en", "en-gb": "en",
+    "chinese": "zh", "mandarin": "zh", "zh-cn": "zh", "zh-tw": "zh", "zh-hans": "zh", "zh-hant": "zh",
+    "japanese": "ja", "jp": "ja", "ja-jp": "ja",
+    "german": "de", "deutsch": "de", "de-de": "de",
+    "spanish": "es", "español": "es", "espanol": "es", "es-es": "es", "es-mx": "es",
+}
+
+_catalog_cache: dict[str, dict[str, str]] = {}
+_catalog_lock = threading.Lock()
+
+
+def _locales_dir() -> Path:
+    """Return the directory containing locale YAML files.
+
+    Lives next to the repo root so both the bundled install and editable
+    checkouts find it without PYTHONPATH gymnastics.
+    """
+    # agent/i18n.py -> agent/ -> repo root
+    return Path(__file__).resolve().parent.parent / "locales"
+
+
+def _normalize_lang(value: Any) -> str:
+    """Normalize a user-supplied language value to a supported code.
+
+    Accepts supported codes directly, common aliases (``chinese`` -> ``zh``),
+    and case-insensitive regional tags (``zh-CN`` -> ``zh``).  Returns the
+    default language for unknown values.
+    """
+    if not isinstance(value, str):
+        return DEFAULT_LANGUAGE
+    key = value.strip().lower()
+    if not key:
+        return DEFAULT_LANGUAGE
+    if key in SUPPORTED_LANGUAGES:
+        return key
+    if key in _LANGUAGE_ALIASES:
+        return _LANGUAGE_ALIASES[key]
+    # Try stripping a region suffix (e.g. "pt-br" -> "pt" won't be supported,
+    # but "zh-CN" -> "zh" will).
+    base = key.split("-", 1)[0]
+    if base in SUPPORTED_LANGUAGES:
+        return base
+    return DEFAULT_LANGUAGE
+
+
+def _load_catalog(lang: str) -> dict[str, str]:
+    """Load and flatten one locale YAML file into a dotted-key dict.
+
+    YAML files can be nested for human readability; this produces the flat
+    key space :func:`t` expects.  Cached per-language for the process.
+    """
+    with _catalog_lock:
+        cached = _catalog_cache.get(lang)
+        if cached is not None:
+            return cached
+
+    path = _locales_dir() / f"{lang}.yaml"
+    if not path.is_file():
+        logger.debug("i18n catalog missing for %s at %s", lang, path)
+        with _catalog_lock:
+            _catalog_cache[lang] = {}
+        return {}
+
+    try:
+        import yaml  # PyYAML is already a hermes dependency
+        with path.open("r", encoding="utf-8") as f:
+            raw = yaml.safe_load(f) or {}
+    except Exception as exc:
+        logger.warning("Failed to load i18n catalog %s: %s", path, exc)
+        with _catalog_lock:
+            _catalog_cache[lang] = {}
+        return {}
+
+    flat: dict[str, str] = {}
+    _flatten_into(raw, "", flat)
+    with _catalog_lock:
+        _catalog_cache[lang] = flat
+    return flat
+
+
+def _flatten_into(node: Any, prefix: str, out: dict[str, str]) -> None:
+    if isinstance(node, dict):
+        for key, value in node.items():
+            child_key = f"{prefix}.{key}" if prefix else str(key)
+            _flatten_into(value, child_key, out)
+    elif isinstance(node, str):
+        out[prefix] = node
+    # Non-string, non-dict leaves are ignored -- catalogs are text-only.
+
+
+@lru_cache(maxsize=1)
+def _config_language_cached() -> str | None:
+    """Read ``display.language`` from config.yaml once per process.
+
+    Cached because ``t()`` is called in hot paths (every approval prompt,
+    every gateway reply) and re-reading YAML each call would be wasteful.
+    ``reset_language_cache()`` clears this when config changes at runtime
+    (e.g. after the setup wizard).
+    """
+    try:
+        from hermes_cli.config import load_config
+        cfg = load_config()
+        lang = (cfg.get("display") or {}).get("language")
+        if lang:
+            return _normalize_lang(lang)
+    except Exception as exc:
+        logger.debug("Could not read display.language from config: %s", exc)
+    return None
+
+
+def reset_language_cache() -> None:
+    """Invalidate cached language resolution and catalogs.
+
+    Call after :func:`hermes_cli.config.save_config` if a running process
+    needs to pick up a changed ``display.language`` without restart.
+    """
+    _config_language_cached.cache_clear()
+    with _catalog_lock:
+        _catalog_cache.clear()
+
+
+def get_language() -> str:
+    """Resolve the active language using env > config > default order."""
+    env_lang = os.environ.get("HERMES_LANGUAGE")
+    if env_lang:
+        return _normalize_lang(env_lang)
+    cfg_lang = _config_language_cached()
+    if cfg_lang:
+        return cfg_lang
+    return DEFAULT_LANGUAGE
+
+
+def t(key: str, lang: str | None = None, **format_kwargs: Any) -> str:
+    """Translate a dotted key to the active language.
+
+    Parameters
+    ----------
+    key
+        Dotted path into the catalog, e.g. ``"approval.choose_long"``.
+    lang
+        Explicit language override.  Takes precedence over env + config.
+    **format_kwargs
+        ``str.format`` substitution arguments (``t("gateway.drain", count=3)``
+        expects a catalog entry with a ``{count}`` placeholder).
+
+    Returns
+    -------
+    The translated string, or the English fallback if the key is missing in
+    the target language, or the bare key if English is also missing.
+    """
+    target = _normalize_lang(lang) if lang else get_language()
+    catalog = _load_catalog(target)
+    value = catalog.get(key)
+
+    if value is None and target != DEFAULT_LANGUAGE:
+        # Fall through to English rather than showing a key path to the user.
+        value = _load_catalog(DEFAULT_LANGUAGE).get(key)
+
+    if value is None:
+        # Last-ditch: return the key itself.  A broken catalog should not
+        # crash anything; it just looks ugly until someone fixes it.
+        logger.debug("i18n miss: key=%r lang=%r", key, target)
+        value = key
+
+    if format_kwargs:
+        try:
+            return value.format(**format_kwargs)
+        except (KeyError, IndexError, ValueError) as exc:
+            logger.warning(
+                "i18n format failed for key=%r lang=%r kwargs=%r: %s",
+                key, target, format_kwargs, exc,
+            )
+            return value
+    return value
+
+
+__all__ = [
+    "SUPPORTED_LANGUAGES",
+    "DEFAULT_LANGUAGE",
+    "t",
+    "get_language",
+    "reset_language_cache",
+]
diff --git a/gateway/run.py b/gateway/run.py
index 433b41387f..c0a6ae0bb1 100644
--- a/gateway/run.py
+++ b/gateway/run.py
@@ -39,6 +39,7 @@ from typing import Dict, Optional, Any, List, Union
 # gateway is a long-running daemon, so its boot cost matters less than
 # preserving the established test-patch surface.
 from agent.account_usage import fetch_account_usage, render_account_usage_lines
+from agent.i18n import t
 from hermes_cli.config import cfg_get
 
 # --- Agent cache tuning ---------------------------------------------------
@@ -7377,7 +7378,7 @@ class GatewayRunner:
         if self._restart_requested or self._draining:
             count = self._running_agent_count()
             if count:
-                return f"⏳ Draining {count} active agent(s) before restart..."
+                return t("gateway.draining", count=count)
             return EphemeralReply("⏳ Gateway restart already in progress...")
 
         # Save the requester's routing info so the new gateway process can
@@ -7429,7 +7430,7 @@ class GatewayRunner:
         else:
             self.request_restart(detached=True, via_service=False)
         if active_agents:
-            return f"⏳ Draining {active_agents} active agent(s) before restart..."
+            return t("gateway.draining", count=active_agents)
         return EphemeralReply("♻ Restarting gateway. If you aren't notified within 60 seconds, restart from the console with `hermes gateway restart`.")
 
     def _is_stale_restart_redelivery(self, event: MessageEvent) -> bool:
@@ -8099,7 +8100,7 @@ class GatewayRunner:
         if lower in ("clear", "stop", "done"):
             had = mgr.has_goal()
             mgr.clear()
-            return "✓ Goal cleared." if had else "No active goal."
+            return t("gateway.goal_cleared") if had else t("gateway.no_active_goal")
 
         # Otherwise — treat the remaining text as the new goal.
         try:
@@ -9317,7 +9318,7 @@ class GatewayRunner:
         try:
             user_config: dict = _load_gateway_config()
         except Exception as e:
-            return f"⚠️ Could not read config.yaml: {e}"
+            return t("gateway.config_read_failed", error=e)
 
         effective = resolve_footer_config(user_config, platform_key)
 
@@ -9350,7 +9351,7 @@ class GatewayRunner:
             atomic_yaml_write(config_path, user_config)
         except Exception as e:
             logger.warning("Failed to save runtime_footer.enabled: %s", e)
-            return f"⚠️ Could not save config: {e}"
+            return t("gateway.config_save_failed", error=e)
 
         state = "ON" if new_state else "OFF"
         example = ""
@@ -10788,7 +10789,7 @@ class GatewayRunner:
         if not has_blocking_approval(session_key):
             if session_key in self._pending_approvals:
                 self._pending_approvals.pop(session_key)
-                return "⚠️ Approval expired (agent is no longer waiting). Ask the agent to try again."
+                return t("gateway.approval_expired")
             return "No pending command to approve."
 
         # Parse args: support "all", "all session", "all always", "session", "always"
diff --git a/hermes_cli/config.py b/hermes_cli/config.py
index 8cf33b90fe..6ca56422e2 100644
--- a/hermes_cli/config.py
+++ b/hermes_cli/config.py
@@ -781,6 +781,11 @@ DEFAULT_CONFIG = {
         "inline_diffs": True,     # Show inline diff previews for write actions (write_file, patch, skill_manage)
         "show_cost": False,       # Show $ cost in the status bar (off by default)
         "skin": "default",
+        # UI language for static user-facing messages (approval prompts, a
+        # handful of gateway slash-command replies).  Does NOT affect agent
+        # responses, log lines, tool outputs, or slash-command descriptions.
+        # Supported: en, zh, ja, de, es.  Unknown values fall back to en.
+        "language": "en",
         # TUI busy indicator style: kaomoji (default), emoji, unicode (braille
         # spinner), or ascii.  Live-swappable via `/indicator <style>`.
         "tui_status_indicator": "kaomoji",
diff --git a/locales/de.yaml b/locales/de.yaml
new file mode 100644
index 0000000000..e0087c651f
--- /dev/null
+++ b/locales/de.yaml
@@ -0,0 +1,24 @@
+# Hermes-Katalog für statische Meldungen -- Deutsch
+# See locales/en.yaml for the source of truth; keep keys in sync.
+
+approval:
+  dangerous_header: "⚠️  GEFÄHRLICHER BEFEHL: {description}"
+  choose_long:     "      [o]einmal  |  [s]sitzung  |  [a]immer  |  [d]ablehnen"
+  choose_short:    "      [o]einmal  |  [s]sitzung  |  [d]ablehnen"
+  prompt_long:     "      Auswahl [o/s/a/D]: "
+  prompt_short:    "      Auswahl [o/s/D]: "
+  timeout:         "      ⏱ Zeitüberschreitung – Befehl wird abgelehnt"
+  allowed_once:    "      ✓ Einmalig erlaubt"
+  allowed_session: "      ✓ Für diese Sitzung erlaubt"
+  allowed_always:  "      ✓ Zur dauerhaften Erlaubnisliste hinzugefügt"
+  denied:          "      ✗ Abgelehnt"
+  cancelled:       "      ✗ Abgebrochen"
+  blocklist_message: "Dieser Befehl steht auf der unbedingten Sperrliste und kann nicht genehmigt werden."
+
+gateway:
+  approval_expired: "⚠️ Genehmigung abgelaufen (Agent wartet nicht mehr). Bitten Sie den Agenten, es erneut zu versuchen."
+  draining:         "⏳ Warte auf {count} aktive(n) Agent(en) vor dem Neustart..."
+  goal_cleared:     "✓ Ziel gelöscht."
+  no_active_goal:   "Kein aktives Ziel."
+  config_read_failed: "⚠️ config.yaml konnte nicht gelesen werden: {error}"
+  config_save_failed: "⚠️ Konfiguration konnte nicht gespeichert werden: {error}"
diff --git a/locales/en.yaml b/locales/en.yaml
new file mode 100644
index 0000000000..283f8cb871
--- /dev/null
+++ b/locales/en.yaml
@@ -0,0 +1,35 @@
+# Hermes static-message catalog -- English (baseline / source of truth)
+#
+# Only user-facing static messages from the CLI approval prompt and a handful
+# of gateway slash-command replies live here.  Agent-generated output, log
+# lines, error tracebacks, tool outputs, and slash-command descriptions stay
+# in English and are NOT translated -- see agent/i18n.py for scope rationale.
+#
+# Keys are dotted paths; nesting below is purely for readability.  Values may
+# contain {placeholder} tokens for str.format substitution.  When adding a
+# new key, add it to EVERY locale file (en/zh/ja/de/es) in the same commit --
+# tests/agent/test_i18n.py asserts catalog parity.
+
+approval:
+  # CLI approval prompt -- shown when a dangerous command needs user review.
+  dangerous_header: "⚠️  DANGEROUS COMMAND: {description}"
+  choose_long:     "      [o]nce  |  [s]ession  |  [a]lways  |  [d]eny"
+  choose_short:    "      [o]nce  |  [s]ession  |  [d]eny"
+  prompt_long:     "      Choice [o/s/a/D]: "
+  prompt_short:    "      Choice [o/s/D]: "
+  timeout:         "      ⏱ Timeout - denying command"
+  allowed_once:    "      ✓ Allowed once"
+  allowed_session: "      ✓ Allowed for this session"
+  allowed_always:  "      ✓ Added to permanent allowlist"
+  denied:          "      ✗ Denied"
+  cancelled:       "      ✗ Cancelled"
+  blocklist_message: "This command is on the unconditional blocklist and cannot be approved."
+
+gateway:
+  # Messenger replies to slash commands and implicit state changes.
+  approval_expired: "⚠️ Approval expired (agent is no longer waiting). Ask the agent to try again."
+  draining:         "⏳ Draining {count} active agent(s) before restart..."
+  goal_cleared:     "✓ Goal cleared."
+  no_active_goal:   "No active goal."
+  config_read_failed: "⚠️ Could not read config.yaml: {error}"
+  config_save_failed: "⚠️ Could not save config: {error}"
diff --git a/locales/es.yaml b/locales/es.yaml
new file mode 100644
index 0000000000..aa7c2c6094
--- /dev/null
+++ b/locales/es.yaml
@@ -0,0 +1,24 @@
+# Catálogo de mensajes estáticos de Hermes -- Español
+# See locales/en.yaml for the source of truth; keep keys in sync.
+
+approval:
+  dangerous_header: "⚠️  COMANDO PELIGROSO: {description}"
+  choose_long:     "      [o]una vez  |  [s]sesión  |  [a]siempre  |  [d]denegar"
+  choose_short:    "      [o]una vez  |  [s]sesión  |  [d]denegar"
+  prompt_long:     "      Opción [o/s/a/D]: "
+  prompt_short:    "      Opción [o/s/D]: "
+  timeout:         "      ⏱ Tiempo agotado — comando denegado"
+  allowed_once:    "      ✓ Permitido una vez"
+  allowed_session: "      ✓ Permitido en esta sesión"
+  allowed_always:  "      ✓ Añadido a la lista de permitidos permanente"
+  denied:          "      ✗ Denegado"
+  cancelled:       "      ✗ Cancelado"
+  blocklist_message: "Este comando está en la lista de bloqueo incondicional y no se puede aprobar."
+
+gateway:
+  approval_expired: "⚠️ La aprobación ha caducado (el agente ya no está esperando). Pida al agente que lo intente de nuevo."
+  draining:         "⏳ Esperando a que terminen {count} agente(s) activo(s) antes de reiniciar..."
+  goal_cleared:     "✓ Objetivo eliminado."
+  no_active_goal:   "No hay objetivo activo."
+  config_read_failed: "⚠️ No se pudo leer config.yaml: {error}"
+  config_save_failed: "⚠️ No se pudo guardar la configuración: {error}"
diff --git a/locales/ja.yaml b/locales/ja.yaml
new file mode 100644
index 0000000000..5cf229a520
--- /dev/null
+++ b/locales/ja.yaml
@@ -0,0 +1,24 @@
+# Hermes 静的メッセージカタログ -- 日本語
+# See locales/en.yaml for the source of truth; keep keys in sync.
+
+approval:
+  dangerous_header: "⚠️  危険なコマンド: {description}"
+  choose_long:     "      [o]今回のみ  |  [s]セッション中  |  [a]常に許可  |  [d]拒否"
+  choose_short:    "      [o]今回のみ  |  [s]セッション中  |  [d]拒否"
+  prompt_long:     "      選択 [o/s/a/D]: "
+  prompt_short:    "      選択 [o/s/D]: "
+  timeout:         "      ⏱ タイムアウト — コマンドを拒否しました"
+  allowed_once:    "      ✓ 今回のみ許可"
+  allowed_session: "      ✓ このセッション中は許可"
+  allowed_always:  "      ✓ 永続的な許可リストに追加"
+  denied:          "      ✗ 拒否しました"
+  cancelled:       "      ✗ キャンセルしました"
+  blocklist_message: "このコマンドは無条件ブロックリストに含まれており、承認できません。"
+
+gateway:
+  approval_expired: "⚠️ 承認の有効期限が切れました（エージェントはもう待機していません）。エージェントに再試行を依頼してください。"
+  draining:         "⏳ 再起動前に {count} 個のアクティブエージェントの終了を待っています..."
+  goal_cleared:     "✓ 目標をクリアしました。"
+  no_active_goal:   "アクティブな目標はありません。"
+  config_read_failed: "⚠️ config.yaml を読み込めませんでした: {error}"
+  config_save_failed: "⚠️ 設定を保存できませんでした: {error}"
diff --git a/locales/zh.yaml b/locales/zh.yaml
new file mode 100644
index 0000000000..7cd9a4f321
--- /dev/null
+++ b/locales/zh.yaml
@@ -0,0 +1,24 @@
+# Hermes 静态消息目录 -- 中文（简体）
+# See locales/en.yaml for the source of truth; keep keys in sync.
+
+approval:
+  dangerous_header: "⚠️  危险命令： {description}"
+  choose_long:     "      [o]仅此一次  |  [s]本次会话  |  [a]永久允许  |  [d]拒绝"
+  choose_short:    "      [o]仅此一次  |  [s]本次会话  |  [d]拒绝"
+  prompt_long:     "      选择 [o/s/a/D]: "
+  prompt_short:    "      选择 [o/s/D]: "
+  timeout:         "      ⏱ 超时 — 已拒绝命令"
+  allowed_once:    "      ✓ 本次允许"
+  allowed_session: "      ✓ 本次会话内允许"
+  allowed_always:  "      ✓ 已加入永久允许列表"
+  denied:          "      ✗ 已拒绝"
+  cancelled:       "      ✗ 已取消"
+  blocklist_message: "此命令位于无条件拦截列表中，无法被批准。"
+
+gateway:
+  approval_expired: "⚠️ 批准已过期（代理不再等待）。请让代理重试。"
+  draining:         "⏳ 正在等待 {count} 个活跃代理结束后重启..."
+  goal_cleared:     "✓ 目标已清除。"
+  no_active_goal:   "当前没有活跃的目标。"
+  config_read_failed: "⚠️ 无法读取 config.yaml：{error}"
+  config_save_failed: "⚠️ 无法保存配置：{error}"
diff --git a/tests/agent/test_i18n.py b/tests/agent/test_i18n.py
new file mode 100644
index 0000000000..1f00e97d45
--- /dev/null
+++ b/tests/agent/test_i18n.py
@@ -0,0 +1,156 @@
+"""Tests for agent.i18n -- catalog parity, fallback, language resolution."""
+
+from __future__ import annotations
+
+from pathlib import Path
+
+import pytest
+import yaml
+
+from agent import i18n
+
+
+LOCALES_DIR = Path(__file__).resolve().parents[2] / "locales"
+
+
+def _load_raw(lang: str) -> dict:
+    with (LOCALES_DIR / f"{lang}.yaml").open("r", encoding="utf-8") as f:
+        return yaml.safe_load(f)
+
+
+def _flatten(d, prefix="") -> dict:
+    flat = {}
+    for k, v in (d or {}).items():
+        key = f"{prefix}.{k}" if prefix else k
+        if isinstance(v, dict):
+            flat.update(_flatten(v, key))
+        else:
+            flat[key] = v
+    return flat
+
+
+# ---------------------------------------------------------------------------
+# Catalog completeness -- this is the key invariant test.  If someone adds a
+# new key to en.yaml they MUST add it to every other locale, else runtime
+# falls back to English for those users and defeats the feature.
+# ---------------------------------------------------------------------------
+
+def test_all_locales_exist():
+    """Every supported language must have a catalog file on disk."""
+    for lang in i18n.SUPPORTED_LANGUAGES:
+        assert (LOCALES_DIR / f"{lang}.yaml").is_file(), f"missing locales/{lang}.yaml"
+
+
+@pytest.mark.parametrize("lang", [l for l in i18n.SUPPORTED_LANGUAGES if l != "en"])
+def test_catalog_keys_match_english(lang: str):
+    """Every non-English catalog must have exactly the same key set as English."""
+    en_keys = set(_flatten(_load_raw("en")).keys())
+    lang_keys = set(_flatten(_load_raw(lang)).keys())
+    missing = en_keys - lang_keys
+    extra = lang_keys - en_keys
+    assert not missing, f"{lang}.yaml missing keys: {sorted(missing)}"
+    assert not extra, f"{lang}.yaml has keys not in en.yaml: {sorted(extra)}"
+
+
+@pytest.mark.parametrize("lang", list(i18n.SUPPORTED_LANGUAGES))
+def test_catalog_placeholders_match_english(lang: str):
+    """Every translated value must use the same {placeholder} tokens as English.
+
+    A mistranslated placeholder (e.g. ``{description}`` typoed as ``{descricao}``)
+    would either raise KeyError at runtime or silently drop the interpolated
+    value.  Pin parity at the test layer.
+    """
+    import re
+    placeholder_re = re.compile(r"\{([a-zA-Z_][a-zA-Z0-9_]*)\}")
+    en_flat = _flatten(_load_raw("en"))
+    lang_flat = _flatten(_load_raw(lang))
+    for key, en_value in en_flat.items():
+        en_placeholders = set(placeholder_re.findall(en_value))
+        lang_value = lang_flat.get(key, "")
+        lang_placeholders = set(placeholder_re.findall(lang_value))
+        assert en_placeholders == lang_placeholders, (
+            f"{lang}.yaml key={key!r}: placeholders {lang_placeholders} "
+            f"don't match English {en_placeholders}"
+        )
+
+
+# ---------------------------------------------------------------------------
+# Language resolution
+# ---------------------------------------------------------------------------
+
+def test_normalize_lang_accepts_supported():
+    assert i18n._normalize_lang("zh") == "zh"
+    assert i18n._normalize_lang("EN") == "en"
+
+
+def test_normalize_lang_accepts_aliases():
+    assert i18n._normalize_lang("chinese") == "zh"
+    assert i18n._normalize_lang("zh-CN") == "zh"
+    assert i18n._normalize_lang("Deutsch") == "de"
+    assert i18n._normalize_lang("español") == "es"
+    assert i18n._normalize_lang("jp") == "ja"
+
+
+def test_normalize_lang_unknown_falls_back():
+    assert i18n._normalize_lang("klingon") == "en"
+    assert i18n._normalize_lang("") == "en"
+    assert i18n._normalize_lang(None) == "en"
+
+
+def test_env_var_override(monkeypatch):
+    """HERMES_LANGUAGE wins over config."""
+    i18n.reset_language_cache()
+    monkeypatch.setenv("HERMES_LANGUAGE", "ja")
+    assert i18n.get_language() == "ja"
+
+
+def test_env_var_normalized(monkeypatch):
+    i18n.reset_language_cache()
+    monkeypatch.setenv("HERMES_LANGUAGE", "Chinese")
+    assert i18n.get_language() == "zh"
+
+
+def test_default_when_nothing_set(monkeypatch):
+    """With no env var and no config override, falls back to English."""
+    monkeypatch.delenv("HERMES_LANGUAGE", raising=False)
+    # Force config lookup to return None -- patch the cached reader.
+    i18n.reset_language_cache()
+    monkeypatch.setattr(i18n, "_config_language_cached", lambda: None)
+    assert i18n.get_language() == "en"
+
+
+# ---------------------------------------------------------------------------
+# t() semantics
+# ---------------------------------------------------------------------------
+
+def test_t_explicit_lang():
+    assert i18n.t("approval.denied", lang="en").endswith("Denied")
+    assert i18n.t("approval.denied", lang="zh").endswith("已拒绝")
+
+
+def test_t_formats_placeholders():
+    msg = i18n.t("gateway.draining", lang="en", count=3)
+    assert "3" in msg
+
+
+def test_t_missing_key_returns_key():
+    """A missing key returns its own path -- ugly but never crashes."""
+    result = i18n.t("nonexistent.key.path", lang="en")
+    assert result == "nonexistent.key.path"
+
+
+def test_t_missing_key_in_non_english_falls_back_to_english(tmp_path, monkeypatch):
+    """If a key exists in English but not in the target locale, fall back."""
+    # Stand up a fake incomplete locale under a temp locales dir.
+    fake_locales = tmp_path / "locales"
+    fake_locales.mkdir()
+    (fake_locales / "en.yaml").write_text("foo: English Foo\n", encoding="utf-8")
+    (fake_locales / "zh.yaml").write_text("# intentionally empty\n", encoding="utf-8")
+    monkeypatch.setattr(i18n, "_locales_dir", lambda: fake_locales)
+    i18n.reset_language_cache()
+    assert i18n.t("foo", lang="zh") == "English Foo"
+
+
+def test_t_unknown_language_uses_english():
+    """Unknown lang codes normalize to English, not to a key-path fallback."""
+    assert i18n.t("approval.denied", lang="klingon") == i18n.t("approval.denied", lang="en")
diff --git a/tools/approval.py b/tools/approval.py
index 4ece3e5be4..a7faaff21f 100644
--- a/tools/approval.py
+++ b/tools/approval.py
@@ -628,15 +628,18 @@ def prompt_dangerous_approval(command: str, description: str,
 
     os.environ["HERMES_SPINNER_PAUSE"] = "1"
     try:
+        # Resolve the active UI language once per prompt so we don't re-read
+        # config/YAML inside the retry loop below.
+        from agent.i18n import t
         while True:
             print()
-            print(f"  ⚠️  DANGEROUS COMMAND: {description}")
+            print(f"  {t('approval.dangerous_header', description=description)}")
             print(f"      {command}")
             print()
             if allow_permanent:
-                print("      [o]nce  |  [s]ession  |  [a]lways  |  [d]eny")
+                print(t("approval.choose_long"))
             else:
-                print("      [o]nce  |  [s]ession  |  [d]eny")
+                print(t("approval.choose_short"))
             print()
             sys.stdout.flush()
 
@@ -644,7 +647,7 @@ def prompt_dangerous_approval(command: str, description: str,
 
             def get_input():
                 try:
-                    prompt = "      Choice [o/s/a/D]: " if allow_permanent else "      Choice [o/s/D]: "
+                    prompt = t("approval.prompt_long") if allow_permanent else t("approval.prompt_short")
                     result["choice"] = input(prompt).strip().lower()
                 except (EOFError, OSError):
                     result["choice"] = ""
@@ -654,28 +657,28 @@ def prompt_dangerous_approval(command: str, description: str,
             thread.join(timeout=timeout_seconds)
 
             if thread.is_alive():
-                print("\n      ⏱ Timeout - denying command")
+                print("\n" + t("approval.timeout"))
                 return "deny"
 
             choice = result["choice"]
             if choice in ('o', 'once'):
-                print("      ✓ Allowed once")
+                print(t("approval.allowed_once"))
                 return "once"
             elif choice in ('s', 'session'):
-                print("      ✓ Allowed for this session")
+                print(t("approval.allowed_session"))
                 return "session"
             elif choice in ('a', 'always'):
                 if not allow_permanent:
-                    print("      ✓ Allowed for this session")
+                    print(t("approval.allowed_session"))
                     return "session"
-                print("      ✓ Added to permanent allowlist")
+                print(t("approval.allowed_always"))
                 return "always"
             else:
-                print("      ✗ Denied")
+                print(t("approval.denied"))
                 return "deny"
 
     except (EOFError, KeyboardInterrupt):
-        print("\n      ✗ Cancelled")
+        print("\n" + t("approval.cancelled"))
         return "deny"
     finally:
         if "HERMES_SPINNER_PAUSE" in os.environ:
diff --git a/website/docs/user-guide/configuration.md b/website/docs/user-guide/configuration.md
index 4c5e51860e..e72d54ef7d 100644
--- a/website/docs/user-guide/configuration.md
+++ b/website/docs/user-guide/configuration.md
@@ -1167,6 +1167,20 @@ display:
   show_cost: false        # Show estimated $ cost in the CLI status bar
   tool_preview_length: 0  # Max chars for tool call previews (0 = no limit, show full paths/commands)
   runtime_metadata_footer: false  # Gateway: append a runtime-context footer to final replies
+  language: en            # UI language for static messages (approval prompts, some gateway replies). en | zh | ja | de | es
+```
+
+### UI language for static messages
+
+The `display.language` setting translates a small set of static user-facing messages — the CLI approval prompt, a handful of gateway slash-command replies (e.g. restart-drain notices, "approval expired", "goal cleared"). It does **not** translate agent responses, log lines, tool output, error tracebacks, or slash-command descriptions — those stay in English. If you want the agent itself to reply in another language, just tell it in your prompt or system message.
+
+Supported values: `en` (default), `zh` (Simplified Chinese), `ja` (Japanese), `de` (German), `es` (Spanish). Unknown values fall back to English.
+
+You can also set this per-session with the `HERMES_LANGUAGE` env var, which overrides the config value.
+
+```yaml
+display:
+  language: zh   # CLI approval prompts appear in Chinese
 ```
 
 | Mode | What you see |