i18n: add LANGUAGES, ACTIVE_LANGUAGES, respond_in_clause helper

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

tests/test_i18n.py

@@ -0,0 +1,44 @@
+"""Unit tests for app.services.i18n."""
+from __future__ import annotations
+
+import pytest
+
+
+def test_languages_contains_all_four_plus_english():
+    from app.services.i18n import LANGUAGES
+    assert set(LANGUAGES.keys()) == {"en", "it", "es", "fr", "de"}
+    assert LANGUAGES["en"] == "English"
+    assert LANGUAGES["it"] == "Italian"
+    assert LANGUAGES["es"] == "Spanish"
+    assert LANGUAGES["fr"] == "French"
+    assert LANGUAGES["de"] == "German"
+
+
+def test_active_languages_is_en_and_it_only():
+    from app.services.i18n import ACTIVE_LANGUAGES
+    assert ACTIVE_LANGUAGES == {"en", "it"}
+
+
+def test_respond_in_clause_empty_for_english():
+    from app.services.i18n import respond_in_clause
+    assert respond_in_clause("en") == ""
+
+
+def test_respond_in_clause_empty_for_none_or_empty():
+    from app.services.i18n import respond_in_clause
+    assert respond_in_clause("") == ""
+    assert respond_in_clause(None) == ""
+
+
+def test_respond_in_clause_italian():
+    from app.services.i18n import respond_in_clause
+    result = respond_in_clause("it")
+    assert "Italian" in result
+    assert result.startswith("\n\n")
+
+
+def test_respond_in_clause_unknown_lang_falls_back_to_english():
+    """Defensive: a raw POST or stale lang code should not crash the
+    prompt assembly. Unknown codes map to no-suffix (English default)."""
+    from app.services.i18n import respond_in_clause
+    assert respond_in_clause("xx") == ""