add(metadata): filter audible results by library language

tests/test_import_flow.py

@@ -647,3 +647,43 @@ def test_append_without_the_flag_is_still_refused(client):
     assert not res["ok"]
     assert "bereits importiert" in res["error"]
     assert (second / "c.mp3").exists()
+
+
+def test_library_language_round_trip(client):
+    lib = client.post("/api/libraries", json={
+        "name": "english", "media_type": "audiobook",
+        "root_path": str(client.tmp_path / "en"), "language": "english",
+    }).json()
+    assert lib["language"] == "english"
+    assert client.get("/api/libraries").json()[0]["language"] == "english"
+
+    # libraries without a language keep working and stay unrestricted
+    other = client.post("/api/libraries", json={
+        "name": "adults", "media_type": "audiobook",
+        "root_path": str(client.tmp_path / "de"),
+    }).json()
+    assert other["language"] == ""
+
+    updated = client.put(f"/api/libraries/{other['id']}", json={
+        "name": "adults", "media_type": "audiobook",
+        "root_path": str(client.tmp_path / "de"), "language": "german",
+    }).json()
+    assert updated["language"] == "german"
+
+
+def test_search_passes_language_to_the_provider(client, monkeypatch):
+    from wordarr.metadata.base import MetadataResult
+    seen = {}
+
+    async def fake(query, language=""):
+        seen["query"], seen["language"] = query, language
+        return [MetadataResult(media_type="audiobook", title="A Game of Thrones",
+                               language="english")]
+
+    monkeypatch.setitem(
+        __import__("wordarr.metadata", fromlist=["PROVIDERS"]).PROVIDERS, "audiobook", fake)
+    res = client.get("/api/search", params={
+        "media_type": "audiobook", "q": "Game of Thrones", "language": "english",
+    }).json()
+    assert seen == {"query": "Game of Thrones", "language": "english"}
+    assert res[0]["language"] == "english"