I work in an industry that has about half Spanish speaking and half English speaking crew members, including a foreman that is ESL. Even though he has great English but especially when flustered or on an off day, his accent can be difficult for my strictly English speaking ears.
I've learned that as long as you speak kindly to anyone, they typically don't mind repeating themselves. I have to slow down at times too and remember things can gets lost in translation as well. As long as you aren't getting frustrated with them, most people want to work with you to communicate effectively.
It's also important to never speak to someone like you think they're stupid for not understanding you (general you). I have some people who roll up in here and act all high and mighty over the fact that they should just understand and speak perfect English. I just side eye them and say "well they know two languages, how many do you know again?" but I'm "not a people person" per my boss