I assume, that characters that work are shared with other languages like Spanish or German and this is why you have them implemented.====All these extra alphabets are part of "utf-8" specification that is being used widely these days in software implementations.
I'd like to chime in on this, if I may:
This is the second time in your posts that you use the phrase "these days" in relation to computer applications, presuming that BBox is one such application - This is a common misapprehension that I see all too often around here, particularly from new users. In this respect BBox simply
isn't like other "these days" kind of applications!
See, unlike most other computer applications "these days", unicode is in fact only
very recently being implemented into BBox, at least on the Mac front, starting only around 2-3 years ago(!!) and this implementation is still not fully completed.
I get the same issues with specific icelandic letters like Þ or ð on my BBox for Mac, so now I simply don't use them anymore when working on this application. The fact that my language is also one of those "rare" ones that don't get 'localised' versions of the application has, as you rightly guessed, much to do with this whole issue.
So there's really only one real "solution" I can give you:
Don't use them!Oh, and NEVER try to save your songs with titles that use anything except ASCII letters! I learned this the hard way (whole songs have gone destroyed!).