Impossible to boot in maybe-ubiquity mode and choose a language when booting in UEFI

When booting Ubuntu or one of its flavors (noticed first with Xubuntu) in UEFI mode, ubiquity never opens. The issue this causes is that there is never a option to choose a language, so all systems booted in UEFI mode are always in English, consequently the language, keyboard and timezone are wrong.

My suggestion is to, instead of having two options (one to try and another to install), have one that boots in the ubiquity window, asking what the user wants to do and the language the user desires to use. Something like:

menuentry "Start Ubuntu" {
 set gfxpayload=keep
 linux /casper/vmlinuz.efi file=/cdrom/preseed/ubuntu.seed maybe-ubiquity boot=casper quiet splash ---
 initrd /casper/initrd.lz
}

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: ubiquity 18.04.9
ProcVersionSignature: Ubuntu 4.15.0-15.16-generic 4.15.15
Uname: Linux 4.15.0-15-generic x86_64
ApportVersion: 2.20.9-0ubuntu6
Architecture: amd64
CasperVersion: 1.393
CurrentDesktop: XFCE
Date: Sun Apr 22 04:28:14 2018
InstallCmdLine: BOOT_IMAGE=/casper/vmlinuz.efi file=/cdrom/preseed/xubuntu.seed boot=casper quiet splash ---
LiveMediaBuild: Xubuntu 18.04 LTS "Bionic Beaver" - Alpha amd64 (20180421.1)
ProcEnviron:
 TERM=xterm-256color
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=C.UTF-8
 SHELL=/bin/bash
SourcePackage: ubiquity
UpgradeStatus: No upgrade log present (probably fresh install)