Honest question: I'd really love to know what UTF-8 traps people fall into all the time when working on a consumer product with Java - especially given that Java basically stores all Strings in UTF-16 (well, starting with Java9+ there's some "optimizations" made, but still). I literally can count those issues on one hand in over a decade of working on such (multilingual) products.
I also completely fail to see what a CRUD app (i.e. java + db) + shooting REST requests to confluence has to do with your concurrency questions, as in interview != job fit, but that might have to do with some missing context.