my friends b-day is in about a month and i wanted sing happy b-day in japanese and swedish.
David has given you the correct text for the birthday song in Swedish – but I guess you’ll need the translation, pronunciation and the melody too.
So that you can make yourself familiar with how it should sound, heres a video from youtube with some Swedish children singing Jag må hon leva. They’re only supposed to do four hoorahs at the end but they get a bit carried away 
If your friend is a girl/female you should use this version:
Sung:
Ja må hon leva, ja må hon leva. (Yes, may she live! Yes, may she live!)
ja må hon leva uti hundrade år! (Yes, may she live for a hundred years)
Ja visst ska hon leva, ja visst ska hon leva, (Of course, she shall live! Of course, she shall live!
ja visst ska hon leva uti hundrade år. (Of course, she shall live for 100 years)
Said:
Ett fyrfaldig leve för …. name of person. (4 cheers for …..
Hon lever! Hurra! Hurra! Hurra! Hurra! (She lives! Hurra Hurra etc)
Pronunciation:
Sung:
Ya moh hoon lay-va (note: lay rhymes with day)
Ya moh hoon lay-va
Ya moh hoon lay-va ootee hoon-dra-day oar
Ya veest ska hoon lay-va
Ya veest ska hoon lay-va
Ya veest ska hoon lay-va ootee hoon-dra-day oar!
Said:
Ett feer-fal-dig lay-ve foeur …. (name of person).
Hoon lay-ver! Hurra! Hurra! Hurra! Hurra!
If your friend is a guy, change the word "hon" (she) to "han" (he) throughout the song.
Don’t worry about the extra verse that David mentioned – not so many people sing that here in Sweden – just occasionally.
Sorry I can’t really help you with Japanese birthday song.