It would be better for me if you spoke to me in English instead of your mother tongue,
Instead of your mother tongue, can you speak to me in English?
I would appreciate it if you spoke to me in English instead of your mother tongue.
❶It would be better for me if you spoke to me in English instead of your mother tongue．
(母語じゃなくて英語で話してくれた方が良いです)。
❷Instead of your mother tongue, can you speak to me in English?
(母語じゃなくて英語で話してくれる？)。
❸I would appreciate it if you spoke to me in English instead of your mother tongue.
(母語じゃなくて英語で話していただけると幸いです)。
＊この言い方が一番丁寧です。
母語ーmother tonge (母の舌)、またはmother language (母の言語)です。
参考までに！
I would appreciate it if you would speak English instead of your mother tongue.
It would be helpful if you could speak English rather than your native language.
I would appreciate it if you would speak English instead of your mother tongue.
「母国語ではなく英語を話して頂けると幸いです。」
「母国語」は mother tongue
It would be helpful if you could speak English rather than your native language.
「母国語ではなく英語を話して頂けると助かります。」
「母国語」は native language とも言えます。
ご参考になれば幸いです！
アメリカ合衆国 
日本 
