It would not be implausible for Hayate to know french, given his association with what amounts to a French empire in modern-day England. But Mordecai and Marduk aren't going to know French.

Nobody but Rhiannon ought to know Welsh.

Hebrew of course is isolated to Mordecai.

Any one of them might have been exposed to Greek because of its prominence in the ancient world.

Arabic is also a decent option, because it's not impossible that the foreigners would learn some Arabic before visiting Jerusalem. 

I'm not really sure about Latin. What's the influence of Latin culture at this point? The Western Roman Empire has collapsed, after all.