I think Verade gave you some good advice!
I think it's also completely okay to say something like "I'm a little nervous because my English is still a work in progress" as you get going, so they person will (I hope) try to remember to speak a little more slowly and clearly.
Everyone is nervous in a job interview. I like also that Verade reminds you that even if this one doesn't go perfectly, it's good practice.
If you are taking any ESL courses, perhaps you can ask your instructor to do role playing with you to help you feel more prepared. Even if you're not taking classes, have someone else pretend to interview you so you can practice forming your answers. Even people who do speak English as their native language do this!