diff --git a/tests/unit/test_language_consistency.py b/tests/unit/test_language_consistency.py
new file mode 100644
index 0000000..b198b76
--- /dev/null
+++ b/tests/unit/test_language_consistency.py
@@ -0,0 +1,40 @@
+from __future__ import annotations
+
+import importlib
+import sys
+import types
+
+
+def _import_language_module():
+    """Import glitter.language with a lightweight rich stub when needed."""
+
+    if "rich.text" not in sys.modules:
+        rich_module = types.ModuleType("rich")
+        rich_text_module = types.ModuleType("rich.text")
+
+        class _FakeText:
+            def __init__(self, value: str) -> None:
+                self.plain = value
+
+            def stylize(self, style: str) -> None:  # noqa: ARG002
+                return None
+
+        rich_text_module.Text = _FakeText
+        sys.modules["rich"] = rich_module
+        sys.modules["rich.text"] = rich_text_module
+
+    return importlib.import_module("glitter.language")
+
+
+def test_message_keys_are_consistent_between_languages() -> None:
+    language = _import_language_module()
+    en_keys = set(language.MESSAGES["en"].keys())
+    zh_keys = set(language.MESSAGES["zh"].keys())
+    assert en_keys == zh_keys
+
+
+def test_message_tones_only_reference_existing_message_keys() -> None:
+    language = _import_language_module()
+    message_keys = set(language.MESSAGES["en"].keys())
+    tone_keys = set(language.MESSAGE_TONES.keys())
+    assert tone_keys <= message_keys