I think many users listen to music in different languages. In my case it's spanish, english, german and french. German and french songs are useful to me to practice. So it would be really nice if I could filter my liked songs by language, because filtering them myself in a playlist would just take so long.
It looks like your idea was posted a while ago but, unfortunately, it hasn't gathered the minimum amount of votes to stay active in the Ideas Exchange (50 votes in the first 3 months). I'll mark your idea as "Closed - Not Enough Votes". You can learn more on how the Ideas Exchange works here.