Not a specialised instance, but these communities are quite active:
An entire instance? A community maybe but even that would surprise me. We barely have active communities for individual TV shows (other than Star Trek). What you’re looking for is a relatively niche interest that Lemmy is still too small to sustain.
Also, what exactly are you looking for? A place to post and find subs? Because I don’t know if you need a community for that when you can just go to opensubtitles or addic7ed or whatever.
https://adultswim.fan/ for adultswim and related programming.
Specialized in subtitles specifically or am I misreading your post title? I can’t imagine there would be with things like OpenSubtitles and the like out there. Very little stuff to discuss with this so a forum for them probably wouldn’t be very active.
