How to edit bootmenu efi on Ubuntu flash drive?

Question

ubuntu

Hello people!
I collected a custom Lubuntu distro on a USB flash drive. I would like it to be custom not only during installation, but also as Live. In principle, everything works, with the exception of an annoying little thing. When booting into EFI, the locale of the menu and OS is English, no choice. When loading into legacy, everything is perfect, the locale is ru by default, the OS is in ru. Because I didn’t collect the flash drive for myself, I would like to fix it. But there is a gap in knowledge. Advise concise man on efi on Linux or just a working solution for live, not deployed OS.
Thank you.