Ok, we all share these words, so I do not know why people are thumbing down people who say it is farsi or urdu or some islamic language. It is very likely that this word is the same in all those languages (including arabic).
I agree with the other guy, yara is like yaar = dude, man, bro in an American way of speaking.
mubarak ~ happy, congratulations, etc.
so people may say things like
Eid mubaarak ~ Happy Eid
Christmas mubaarak ~ Merry Christmas
or in this case
yara mubaarak ~ congratulations, man/bro/dude/whatever
People are saying this is an arabic name as well, so if this is someone's name then, it is like "congratulations yara"