The last part is a little easier if you're in a context where other people either don't speak English or are unconfident in it. Many Spanish people will be okay interacting with your broken Spanish, for example, but many (most?) Scandinavians will immediately switch to English. I've also had better luck with languages which have more speakers, since they're more used to hearing non-native accents: French or Spaniards or Italians can accept a pretty wide range of pronunciations, but mispronounced Danish ends up completely unintelligible to many people.
mm, the only place I've put this into practice was when I was learning French and living in Quebec, I'd simply say that I was trying to practice and most people would go along with it. I can see it being a problem if your bad accent makes the language unintelligible though.
