When I was in Copenhagen (Denmark), I was impressed by the dialog of some other tourists with our host. They both spoke their native Scandinavian languages (noteworthy to say I understand no Scandinavian languages but I believe I can recognize that they are actually spoken), but it sounded like they speak different languages.
The only I have understood was a relatively large number of English words they used in their conversation. Is it a common practice to communicate this way? So, what is the more polite and effective way for a Swede to start communication with a Dane: to start speak pure English or to start speak his native language, adding English words when you doubt your interlocutor understand you?