Not sure what you mean by “advanced caching”. There is some basic caching for data which rarely or never changes, for example most things in /api/v3/site. But other data like post listings change a lot, so caching is not an option and instead its a matter of optimizing the sql queries (using the right indexes, reducing the number of joins, making benchmarks and looking at query plans).
Here is an issue on this topic: https://github.com/LemmyNet/lemmy/issues/5555







What you should do as a mod is set the allowed languages in the community settings. Then people wont be able to post in other languages. Though I realize that the UI for this isnt so good for now.