Rudi, amen.
I agree very much with what you are saying. We don't always recognize that what may be completely correct English can be tough to interpret if you are not native/fluent.
As many of you know I work with Latin Americans a lot. Many of them have studied in the USA, but I always reread my emails and memos to them. I always find things to simplify.
Remember communication is a 2 way street--it does no good if you do it unilaterally!!!
(recent flight from Curacao to Miami--the AA flight purser spoke so fast (English) that even us monolinguals were having trouble understanding. We finally pulled the flight attendant who was doing the pantomime aside to tell her to get him to slow it down. It was particularly inappropriate for an international flight to a non-English speaking island).