feat: add runtime i18n API with manifest translations

lib/runtime/scripting/lua_dardo_script_engine.dart

@@ -71,6 +71,69 @@ class LuaDardoScriptEngine implements ScriptEngine {
     }
   }
 
+  @override
+  void setTranslations({
+    required String locale,
+    required Map<String, Map<String, String>> translations,
+  }) {
+    _lua.getGlobal('runtime');
+    if (_lua.isNil(-1)) {
+      _lua.pop(1);
+      return;
+    }
+
+    _lua.newTable();
+
+    _lua.pushString(locale);
+    _lua.setField(-2, 'locale');
+
+    _lua.pushDartFunction((LuaState lua) {
+      lua.pushString(locale);
+      return 1;
+    });
+    _lua.setField(-2, 'get_locale');
+
+    _lua.pushDartFunction((LuaState lua) {
+      final key = lua.toStr(1);
+      if (key == null || key.isEmpty) {
+        if (lua.getTop() >= 2 && !lua.isNil(2)) {
+          lua.pushValue(2);
+        } else {
+          lua.pushString(key ?? '');
+        }
+        return 1;
+      }
+
+      final localeDict = translations[locale];
+      final value = localeDict?[key];
+      if (value != null) {
+        lua.pushString(value);
+        return 1;
+      }
+
+      for (final entry in translations.entries) {
+        if (entry.key != locale) {
+          final fallbackValue = entry.value[key];
+          if (fallbackValue != null) {
+            lua.pushString(fallbackValue);
+            return 1;
+          }
+        }
+      }
+
+      if (lua.getTop() >= 2 && !lua.isNil(2)) {
+        lua.pushValue(2);
+      } else {
+        lua.pushString(key);
+      }
+      return 1;
+    });
+    _lua.setField(-2, 't');
+
+    _lua.setField(-2, 'i18n');
+    _lua.pop(1);
+  }
+
   @override
   bool smokeTest(Map<String, Object?> context) {
     _lua.getGlobal('smoke_test');

lib/runtime/scripting/script_engine.dart

@@ -22,4 +22,10 @@ abstract interface class ScriptEngine {
   GameDiff init(Map<String, Object?> context);
 
   GameDiff dispatchEvent(RuntimeEvent event);
+
+  /// 设置翻译字典和当前语言，Lua 侧可通过 runtime.i18n.t(key, fallback) 查询。
+  void setTranslations({
+    required String locale,
+    required Map<String, Map<String, String>> translations,
+  });
 }