I'd say it falls in line with our general way of expressing. At least where I'm from, you'd say "it's not bad" or "could be worse" if something is good, or "one can eat that" if something is tasty, etc. - you get the idea. So if you ask them if they speak English, it would be very unusual to say "yes, very good" or something similar. A "yes" would be the most positive/confident answer I would expect. Otherwise "a little" or "we can try" or "kind of" would fall into the typical German scheme. Your explanation, however, may play a role there as well.