Question about changing the language and domain on the forum.

[Agentos]

I'm thinking very hard about changing the language of the forum and domain, but I don't know how it will look like with posts in the native language. English will be the main language and old threads would be moved, for example, to the archive category. What does SEO look like after such changes? I know that I will definitely have to redirect from the old domain to the new one, but the most interesting thing for me is how Google will see all this. Why do I want to make these changes? This will allow me to reach a wider group of recipients around the world. Let me know what you think about it. Thanks in advance for any advice.