Locale issues:
* Environment strings have unspecified encoding.
* File names ditto. (Which matters when they get printed together with other
strings.)
* gecos information ditto.
If, and if only, you[*] call setlocale:
* ctype stuff.
* strtod, printf %[efg]
* Regexps
(Integer parsing and printing seems to be safe in pratice if not in theory.)
If you call system() you also need to watch out for things like Gnu sort
being locale sensitive.
Morten
[*] That would be not just you, but also all the yous behind all the
libraries you link.