Should I simplify my writing in a foreign country?
Thou shalt not dumb down thy writing, but don't make it a vain exercise of style

I'm a non-native English speaker, and let me put it straight: I may write in simple English, because limited are my English writing skills, but I don't want to read simple English because I want to enrich my vocabulary and grammatical constructions. 

But whether you write for a native English speaker or not, write clearly, avoiding unnecessary verbosity just to show off your eloquence.

(And, honestly, stop wasting time using those readability tests)