diff --git a/strix.spec b/strix.spec
index 827e5e2c..fad16499 100644
--- a/strix.spec
+++ b/strix.spec
@@ -36,6 +36,10 @@ for asset in viewer_static.rglob('*'):
         rel_path = asset.relative_to(project_root)
         datas.append((str(asset), str(rel_path.parent)))
 
+for json_locale in strix_root.rglob('locales/*.json'):
+    rel_path = json_locale.relative_to(project_root)
+    datas.append((str(json_locale), str(rel_path.parent)))
+
 datas += collect_data_files('tiktoken')
 datas += collect_data_files('tiktoken_ext')
 
@@ -112,6 +116,7 @@ hiddenimports = [
 
     # Strix modules
     'strix',
+    'strix.i18n',
     'strix.interface',
     'strix.interface.main',
     'strix.interface.cli',
diff --git a/strix/agents/prompts/system_prompt.jinja b/strix/agents/prompts/system_prompt.jinja
index 23493d2d..f545a08e 100644
--- a/strix/agents/prompts/system_prompt.jinja
+++ b/strix/agents/prompts/system_prompt.jinja
@@ -1,4 +1,9 @@
 You are an advanced AI application security validation agent. Your purpose is to perform authorized security verification, reproduce and validate weaknesses on in-scope assets, and help remediate real security issues.
+{% if language_directive %}
+<language_directive>
+{{ language_directive }}
+</language_directive>
+{% endif %}
 You follow all instructions and rules provided to you exactly as written in the system prompt at all times.
 {% if is_root %}
 <root_agent_directive>
diff --git a/strix/config/settings.py b/strix/config/settings.py
index 42a2c97e..0e20af47 100644
--- a/strix/config/settings.py
+++ b/strix/config/settings.py
@@ -147,6 +147,10 @@ class ViewerSettings(BaseSettings):
 class Settings(BaseSettings):
     model_config = _BASE_CONFIG
 
+    language: str = Field(
+        default="en",
+        validation_alias=AliasChoices("STRIX_LANGUAGE", "language"),
+    )
     llm: LlmSettings = Field(default_factory=LlmSettings)
     dedupe: DedupeSettings = Field(default_factory=DedupeSettings)
     runtime: RuntimeSettings = Field(default_factory=RuntimeSettings)
diff --git a/strix/i18n.py b/strix/i18n.py
index 07a0ab6b..0a280291 100644
--- a/strix/i18n.py
+++ b/strix/i18n.py
@@ -45,11 +45,13 @@ def get_language() -> str:
 
 
 def _detect_language() -> str:
-    """Detect language via STRIX_LANGUAGE, config file, or system LANG."""
+    """Detect language via STRIX_LANGUAGE, config file, or system LANG/LC_ALL."""
+    # 1. Environment Variable STRIX_LANGUAGE
     env_lang = os.getenv("STRIX_LANGUAGE")
     if env_lang:
         return _normalize_lang(env_lang)
 
+    # 2. Config File ~/.strix/cli-config.json
     try:
         cfg_path = Path.home() / ".strix" / "cli-config.json"
         if cfg_path.exists():
@@ -60,7 +62,8 @@ def _detect_language() -> str:
     except Exception:
         pass
 
-    sys_lang = os.getenv("LANG") or os.getenv("LC_ALL")
+    # 3. System Locale (LC_ALL takes precedence over LANG)
+    sys_lang = os.getenv("LC_ALL") or os.getenv("LANG")
     if sys_lang:
         return _normalize_lang(sys_lang)
 
@@ -68,24 +71,32 @@ def _detect_language() -> str:
 
 
 def _load_locale(lang: str) -> Dict[str, str]:
-    """Load locale JSON file with thread-safe caching and user overrides."""
+    """Load locale JSON file with thread-safe caching, type validation, and user overrides."""
     with _locales_lock:
         if lang in _locales_cache:
             return _locales_cache[lang]
 
     translations: Dict[str, str] = {}
 
+    def _safe_merge(source_data: Any) -> None:
+        if isinstance(source_data, dict):
+            for k, v in source_data.items():
+                if isinstance(k, str) and isinstance(v, str):
+                    translations[k] = v
+
+    # Built-in locale
     builtin_path = Path(__file__).parent / "locales" / f"{lang}.json"
     if builtin_path.exists():
         try:
-            translations.update(json.loads(builtin_path.read_text(encoding="utf-8")))
+            _safe_merge(json.loads(builtin_path.read_text(encoding="utf-8")))
         except Exception:
             pass
 
+    # User override locale (~/.strix/locales/{lang}.json)
     user_path = Path.home() / ".strix" / "locales" / f"{lang}.json"
     if user_path.exists():
         try:
-            translations.update(json.loads(user_path.read_text(encoding="utf-8")))
+            _safe_merge(json.loads(user_path.read_text(encoding="utf-8")))
         except Exception:
             pass
 
diff --git a/strix/interface/cli_args.py b/strix/interface/cli_args.py
index 6c672437..af0563d4 100644
--- a/strix/interface/cli_args.py
+++ b/strix/interface/cli_args.py
@@ -50,6 +50,13 @@ def _positive_int(value: str) -> int:
 
 
 def parse_arguments() -> argparse.Namespace:
+    # Pre-resolve language before argparse if set in sys.argv
+    for idx, arg in enumerate(sys.argv[:-1]):
+        if arg in ("--language", "-l") and idx + 1 < len(sys.argv):
+            from strix.i18n import set_language
+            set_language(sys.argv[idx + 1])
+            break
+
     parser = argparse.ArgumentParser(
         description="Strix Multi-Agent Cybersecurity Penetration Testing Tool",
         formatter_class=argparse.RawDescriptionHelpFormatter,
@@ -108,6 +115,12 @@ Examples:
         help="Update strix to the latest version and exit. Self-updates the "
         "standalone binary install; for pip/pipx/uv installs, prints the "
         "matching upgrade command instead.",
+    parser.add_argument(
+        "--language",
+        "-l",
+        type=str,
+        default=None,
+        help="Language preference for CLI messages and audit reports (e.g. en, es, id)",
     )
 
     parser.add_argument(