I know Japanese (kind of a major language of the era) and will start French and German in college this semester. Also, I know English…

As far as I can tell (and I don’t know much) you can kind of split World War II into two areas and the resulting languages therein:

The West:

English (x)
French
German
Polish
Italian
Russian

The East:

Japanese (x)
Chinese (Mandarin, at least)
English (x)
Korean
Tagalog
Vietnamese

I’ve kinda got my work cut out for me, eh?