Sounds like you got a Middle East version probably, rather than a truly international one. What model number is it? Samsung devices sold in China only have Chinese, Korean and English. Normally Android includes many languages, including Cyrillic languages, and the main Middle Eastern languages as well. Don't know about flashing a different official Samsung ROM, someone else might have to come in here. You could load it with an aftermarket ROM like CyanogenMod, which does include Cyrillic languages.
AFAIK language options for Android are done when a software ROM is compiled/built.