redravin, I agree with your friend to some point
Japanese people (generally speaking, of course) try to be polite, not by just congugating their verbs -imasu, but also by being indirect (in some cases, extremely indirect); it's a form of being humble, by not directly stating what you have to say, but making it understood, even if it takes more (or less) words to say. Generally speaking what 'shirimasen!' would be understood to be (After already asking anatatachi wa nihongo ga wakarimasu ka) would be something like the following:
I don't know (if you understand japanese, but could find out by you telling me).
Admittingly, instead of wakarimasu ne, I should have probably used 'wakatte imasu ne'... in which case it would have translated to:
You're understanding me (aren't you?)
Same idea behind using the particle 'no' with suru. Not the best idea I understand, but if I was to say 'nihongo no benkyo shite!' (I'm currently studying/learning japanese), I believe it would be perfectly acceptable. After all, japanese _is_ what I'm learning..
But again, I appreciate his input, and as usual, i'm probably completely wrong
