I do quite a few talks for work with non-native english speakers. They are pretty good english speakers in general, but it's still easy for them to get lost especially if it gets conversational with multiple people.

Initially I took to putting more text on the slides to counter that and give them some words to lock onto if they weren't catching the word or otherwise something to follow. This helped to some extent but I have since learnt what works better is to write a lot more into the "Speaker Notes" and distribute a copy of the file to them before the talk starts. Then they can follow along and when they get lost look at the speaker notes to try and get themselves in sync.