оба первых ответ принимаются. Первый потому что грубовато, второй. потому что более литературно. .Еще бы "с местными идеоматическими выражениями... "
Speak your native language. That's easier to understand than your broken English.
speak in his own language, it is easier to understand than your broken English
omg, зачем так грубо! Скажите так: Speak your native language, it will be easier to understand for me.
You'd better speak your native language than your broken English
Speak in your native language. It's easier to understand for me than your bad English.
Speak (in) your native language. It's easier for me to understand your native language instead of your broken English
Do you mind using your native language with me? I have difficulties with getting you, when you speak English.
Англоязычные намного вежливей, чем русскоязычные, поэтому старайтесь не использовать приказной тон по возможности.
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