Fix TTS speaker typo and add supported languages (#990)

Signed-off-by: linyueqian <linyueqian@outlook.com>

tests/entrypoints/openai_api/test_serving_speech.py

@@ -308,7 +308,7 @@ class TestTTSMethods:
         assert speech_server._validate_tts_request(req) == "Input text cannot be empty"
 
         # Invalid language
-        req = OpenAICreateSpeechRequest(input="Hello", language="French")
+        req = OpenAICreateSpeechRequest(input="Hello", language="InvalidLang")
         assert "Invalid language" in speech_server._validate_tts_request(req)
 
         # Invalid speaker