Pocket TTS ships one model per language, but LoadModel called
TTSModel.load_model() with no arguments, so the library always fell back
to its English model whatever the model config said. Read a `language`
option and pass it to load_model, keeping the library default when it is
not set. Document the option and add unit tests that mock the loader.
Fixes#12759
Assisted-by: Claude:claude-opus-5-5
Younes Beriane