A few years ago, a German consultant came over to join our meeting in Taiwan, and we always speak local language occasionaly. The German consultant always remind us "Speak in English, please!" seriously.
Since that day , I used to say：
"I am a native speaker in Chinese"
"He is a native speaker in German"
"I am not a native speaker in English"
German consultant however is not a native speaker in English either.
I would like to know if I can say:
"I am not a native speaker in English" ?
or just say
"I am not a native speaker" ?
or something else?
Furthermore, German consultant sometime emphasized in short:
"In English , please!"
Is that okay to a native English speaker or not?