diff --git a/libretranslate/tests/test_api/test_language_variant_fallback.py b/libretranslate/tests/test_api/test_language_variant_fallback.py
new file mode 100644
index 0000000..b28a046
--- /dev/null
+++ b/libretranslate/tests/test_api/test_language_variant_fallback.py
@@ -0,0 +1,50 @@
+import sys
+import pytest
+from libretranslate.app import create_app
+from libretranslate.main import get_args
+
+
+@pytest.fixture()
+def app_with_pb():
+    sys.argv = ['', '--load-only', 'en,pb']
+    app = create_app(get_args())
+    yield app
+
+
+@pytest.fixture()
+def client_with_pb(app_with_pb):
+    return app_with_pb.test_client()
+
+
+@pytest.fixture()
+def app_with_pt():
+    sys.argv = ['', '--load-only', 'en,pt']
+    app = create_app(get_args())
+    yield app
+
+
+@pytest.fixture()
+def client_with_pt(app_with_pt):
+    return app_with_pt.test_client()
+
+
+def test_portuguese_fallback_pb_to_pt(client_with_pt):
+    response = client_with_pt.post("/translate", data={
+        "q": "Hello",
+        "source": "en",
+        "target": "pb",
+        "format": "text"
+    })
+    
+    assert response.status_code == 200
+
+
+def test_portuguese_fallback_pt_to_pb(client_with_pb):
+    response = client_with_pb.post("/translate", data={
+        "q": "Hello",
+        "source": "en",
+        "target": "pt",
+        "format": "text"
+    })
+    
+    assert response.status_code == 200