[BUG] Unable to properly recognize language in MKV container

[Dan64]

I can look into adding non tagged streams if 'Undef (und - un)' is selected, but always including streams without tags will not happen.

The problem is that in mp4/avi containers the language tag can be unspecified, not available. The mkv is more robust and don't allows to don't specify the language tag and [und] is automatically added or enforced. So your management of  'Undef (und - un)'  should included all these situations. But in this case could be better to add an option in Automation to always included indeterminate language streams.