Searches: "Russian speakers in Finland," "Russian + Finland + bilingualism," the previous along with qualifiers like "1930s", and similar, mainly turning up modern-day information about Russian immigrants. Also tried Googling Winter War and Continuation War interpreters.
I have a Finnish character, about twenty-four, probably not super-highly educated (at least in a formal setting) but quite curious, quite bright, and very motivated. Part of the plot as it's shaping up is that he's sent into a particular situation because he can speak (and read) some degree of Russian (plot-wise, so his nonviolent interaction with a younger and not-much-more-educated Russian character won't be restricted to charades and that whole point-at-various-things-and-say-their-na
I'm guessing it won't be too much of a long shot seeing as Russia's next door - am I wrong? Would it be rare? Conversely, did everyone and their dog know some (in which case he has other qualifications to pull out for the job)?
Thanks in advance!
ETA: Wow. At this point I've got a lot of food for thought and further ideas on where I'm taking this thing. Thanks again for all your help!