I've been using GNOME shell for a long while, and still can't find a fix for this. There are certain fonts (like Roboto, Lucida Grande, among others) displaying tildes wrong, also with eñes (n with a hypen :P) For example:
Configuraci ó n - Some sentence with the e ñ e letter
Configuraci 'o n - Some sentence with the e ~n e letter.
I searched forums a bit, but since this problem isn't showing up on english machines, then I couldn't get any specific fix.
Any Ideas? Thanks!