I think Mochizuki won't have any problems with English, since he spent his school days, up to PhD in the US.

https://en.wikipedia.org/wiki/Shinichi_Mochizuki

About Hoshi, I have seen him in a conference video before, and have an impression that he isn't good at English, which can make a bit difficult in discussion.

I don't know about Scholze and Stix.