Might as well say it so it is understandable by all the local forums too:
Happy holidays, felices fiestas, اجازة سعيدة, Selamat berlibur, 節日快樂, sretni praznici, frohe feiertage, ευχάριστες διακoπές, חג שמח, bonne fêtes, buone vacanze, खुश छुट्टियाँ, 幸せな休日, fijne feestdagen, 행복한 휴일, masaya pista opisyal maligayang kapistahan, Wesołych świąt, boas festas, cчacтливыx пpaздникoв, sărbători fericite, glædelig ferie, lykkelig ferie, glada helgdagar, iyi tatiller, ...
Note: I may have screwed-up on a few though.
Edit: @jonemil24, I'll take your word over Google's for it ...
Good effort on your part, but in our local language we will not say "Sretni praznici" but ''Sretni blagdani'' or even better ''Sretan Božić''.
Merry Christmas everyone!