I work with Germans, Italians, Spaniards, French, Dutch and I understand them 99% of the time. We use "normal" words (we are not fancy regarding vocabulary) and pronounce them in a non-native way (the way all Europeans that speak English understand)... But the moment our British colleagues join the conversation, then our understanding decreases to around 70%: either because of the usage of "fancy" words or because of pronunciation.
Besides, since we all make the same mistakes when speaking English, we understand each other without asking "sorry, what do you mean?"