Korean. Its FAR easier than any of the other lanuages you're considering. You could probably get to a profiecient level quickly enough that you could take up study in the two other languages you left behind.
Plus, the chicks are hot 8)
I'd reccomend against japanese just because it would make you look like a weeaboo faggot, and you'd probably lose interest after awhile.
Arabic can be fun, but the cript is hard. On the plus side, you'll be able to find work as a translator incredibly easy.