mbrtowc() and the functions in iofwide.c are stubs, IOW they don't do anything at the moment.
I tried to uncomment the #if 0'ed code in there, but the code doesn't compile (doesn't link, actually) because we have a mix of glibc versions: for example, the code in "locale" is from glibc 2.2.5, while the rest is more recent.
I think this mix was done because more recent glibcs don't compile with our gcc (at least, Jerome said so) :)
What should we do now ? Mix'n match some more until we get to a working situation ? mbrtowc.c from 2.2.5 works, at least, but then there is also iofwide.c which looks a bit more integrated with the rest (I haven't tried yet its 2.2.5 equivalent).