The latin variant of the Serbian locale sr_CS@Latn is missing in glibc-2.3.90-30 that comes with FC5test2. Also, the existing sr_CS one (cyrillic) seems to default to iso85595 instead of utf8. More info on up-to-date Serbian locales can be found at the link provided.
sr_CS can't use UTF-8 charset, once a locale has some charset, it must never change. If you want UTF-8 sr_CS, you should use sr_CS.UTF-8. As for sr_CS@Latn, you should report this upstream and get it included into upstream glibc, then it will make it into Fedora glibc automatically. See http://sources.redhat.com/bugzilla/