Hey, I think I thought of a way to localise the joke!
On female byleth you say "My name is said as 'Beles'"
The people say "I bet we should call you Beles as well, huh?"
And on male one you say "No, you say mine as 'Beleth'."
So? So? Does it make sense? Did it work?!
....Okay I may have gotten a bit too enthusiastic about it, but I do wonder if it works, though... o3o"