First of all, you should gain an understanding of their level of English, many non-native Speakers actually have a native level of English.
If you feel that your speaker struggles to understand you, you should speak clearly, not use slang or short forms (cannot rather than can't, going to rather than gonna) and use more simple words.
C.twice with smaller movemennt
the only political system that could guarantee the cooperation between the legislative and executive branches is a dictatorship