It's just the internal names that have to be basic letters, numbers and underscores, if that's what you mean. You can set the display names to anything you like:
game Dïåcritics
id diacritics
room hagatna You're in downtown Hagåtña.
thing cajon Cajón
name cajón
loc hagatna
verbs play
verb play cajon
display plåy
prompt plåy {$this}
say It sounds better than Motörhead!