I am looking to have EN show up in episode names when the language is only English while using the {MediaInfo AudioLanguages} naming tag. I noticed it will show up when using {MediaInfo Full}, but not {MediaInfo AudioLanguages}. I was going to submit this as a bug but it seems intended according to this comment by the Sonarr team:
My main need for it is identifying anime episodes if they are JA, EN, or JA+EN from the file name. I use the identifier in the file name to track what shows I have what languages for. I could just assume its english only if there isn’t a tag but its just a one-off I have to manage then.