Ok, so the localization project is for the compiler itself -- rather than the server-side of things -- there is one thread about it already over here: Gsoc2020 Localization of Compiler Diagnostic Messages
You can either start your own thread or join the existing one and ask @xedin for advice with regards to that specific project, as he's the mentor for that one (as can be found out on Swift.org - Project Ideas for GSoC 2020 )
Hope this helps.