If it's something that are requirements for learning other stuffs, flip that idea around:
Give them out as bonus skills when PCs learn that thing they want. (eg. you learn 六指琴魔, you get 音律 as bonus. Or in a more straightforward way, let PC use 六指琴魔 to make 音律 checks.)
If it isn't... What's the point of making that a skill if you don't see PCs use them?
Many systems have the "come up with your own skill" rules.
Or the "character quirk" rules for people who want to master
Fierljeppen, which AFAIK isn't a skill in any games (unless it's some Finnish RPG I don't know about)
Or group it in "Profession(Specify)", "Education(Specify)" & "Hobby(Specify)" skills.
Give them options to have a skill that is useless but personal, instead of making a splatter-list of skills and hope they'll choose one. (Which actually does lead to some GMs trying to force PCs to take certain skills they don't want, and that's kinda a problem too...)
A huge skill list isn't necessarily a good thing. Lots of games post-2010 actually try to shrink that as much as possible, just saying.
