Formal:
* हिंदी मत बोलो (Hindi mat bolo): This is the most direct and polite way to say it. It literally translates to "Don't speak Hindi".
* हिंदी में बात मत करो (Hindi mein baat mat karo): This means "Don't speak in Hindi".
* कृपया हिंदी में बात न करें (kripya Hindi mein baat na karen): This is a more formal and respectful way to say "Please don't speak Hindi".
Informal:
* हिंदी मत बोल (Hindi mat bol): This is a more casual way to say "Don't speak Hindi".
* हिंदी में बात मत कर (Hindi mein baat mat kar): This means "Don't speak in Hindi".
Other ways to express the same sentiment:
* मुझे हिंदी समझ में नहीं आती (mujhe Hindi samajh mein nahin aati): This means "I don't understand Hindi".
* क्या आप अंग्रेजी बोल सकते हैं? (kya aap angrezi bol sakte hain?): This means "Can you speak English?".
Important Note: It's important to be mindful of the context and your relationship with the person you're speaking to when choosing how to express this.