Language identification

I have lots of audio files in different languages and I'd like to run them through Vosk to find out which ones contain Russian speakers. I think I can get close by using the Russian model and word level confidences. But running an English audio file with the same Russian model also returns a lot of results. The confidences are lower than using the Russian model, but not enough to be certain.

How can I find the number words in an audio file that are NOT detected? For example, I have an English audio file that returns 60 words when using an English model, but returns 30 words running the same file through the Russian model. It might be useful to know how many words aren't found or have a zero word confidence level. Is that possible? I haven't found anything in the code or examples that do that.

More generally, what's the best way to reasonable determine programmatically that the language is Russian? I'd like to do the same for other languages such as Chinese.