[Feature] Detect unknown and/or listed audio track languages to mark as bad

[phobiac]

Is your feature request related to a problem? Please describe.
I occasionally get video files where the audio track is listed as having an unknown language. This causes problems that have fairly easy workarounds (primarily, when choosing if subtitles should be played the assumption is that unknown audio track languages are not English) but it would be great to easily identify these files and checkrr seems like it could potentially do this.

Describe the solution you'd like
I was hoping this could be resolved similar to #84, but using something like a removelang list in the config file. Finding video files with unknown language audio tracks is my main concern, but if there's some way to expand that out to setting custom languages that seems like it could be useful.

Describe alternatives you've considered
This complicates the feature and maybe should be asked for as a different enhancement, but it would be useful if checkrr's Bad Files list had a column documenting why the file was marked as bad. For this language detection feature it would help to differentiate between the various reasons a file could be marked as bad.

[phobiac]

I explored solving this with a script and wanted to share that ffprobe has mildly unexpected behavior when the language tag is not defined and it returns a null. If you're using ffprobe to test for unknown or undefined language tags you can leverage the csv output option to return something that can be more easily caught by grep. Not sure how you'd want to implement this check but here's the command I ended up with.

ffprobe -v quiet -select_streams a -show_entries stream_tags=language -of csv=p=1:nk=0 "{}" | grep -q -w "stream,"

[phobiac]

Just wanted to say it's awesome that you added this, thank you!