Try to Support the XTTS-v2 in Multilingul Cases

[SunAriesCN]

Try to support the XTTS-v2 in multilingul cases, because XTTS-v2 models may not has the num_speakers and num_languages variables.

The reproduce way is run the following command

python3 TTS/server/server.py \
    --model_name tts_models/multilingual/multi-dataset/xtts_v2 \
    --config_path /root/.local/share/tts/tts_models--multilingual--multi-dataset--xtts_v2/config.json \
    --model_path /root/.local/share/tts/tts_models--multilingual--multi-dataset--xtts_v2 \
    --use_cuda true \
    --show_details true

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