Go ahead and talk to them. They're polite so they won't reject or ignore you. If you talk to them in Japanese they'll normally be surprised and say ええ～日本語話せるんですか？すごい～or something like that, because we normally don't expect non-Japanese people to speak Japanese. They're mostly shy, so they won't start a conversation if you don't talk to them first, and when they don't know English (or the language spoken in the country) they're shyer I think... But I think they're traveling abroad because they're interested in foreign cultures and people, so I think they'd be happy to talk to and get to know new people.

Don't care about the gramma a lot. The comminication with japanese are very important. I have a lot of friends from latin amrecia. I just learned spanish 3 weeks. but I like talk with them in spanish. To be honest I also learned english by myself. And never go to any english training school. My english is not very good. But I can make a lot friends from all around world. I think its enought for me.

That's exactly what I feel!