Store lang_id in context

[kamranjon]

This stores the language id in the context. This is useful if you are using the auto detect language feature, and want access to the language after the running whisper_full.

I am not very familiar with C++ so feel free to ignore this if it is not the correct approach. If you do know another way to access this value without having to rerun the language detection with whisper_lang_auto_detect, it would be great if you could share that information with me.

With this code you can do something like this:

whisper_lang_str(whisper_full_lang_id(ctx));

After running whisper_full - to get a string like en or cs