> Do you really want the English guy to forget 2/3 of his native language just to please others?
Communication is about exchanging information. If you're this English guy and you're blabbing something and no one understands you, would you be fine with being not understood (i.e. your information being lost)? If so, why even open your mouth?
GP's scenario is about people in Continental Europe. If the English knowledge is weak, an English person speaking in idioms (e.g. https://www.youtube.com/watch?v=awUqKKEKQh4 ) would confuse them quite easily.