For an English language learner to really find success, there's a great amount of research that proves that they should first be strong in their mother tongue (or first language). Some feel the need to just talk English at home, but in actual fact, keeping your child's first language strong is very important if they are learning English. It allows them to build content understanding first, and then have something to attach their ideas to when they move over into English.
A simple example: Imagine learning about colours in English (as a learner who's new to English) if you've never learnt about them in the language that you're most comfortable in - it would be hard, wouldn't it!
How do you incorporate different languages at home?