A bug that bricks your device... fascinating. Since I have just flashed a device with GrapheneOS but haven't set it up yet, I decided to try it out, since I could hardly believe it.
The pseudo languages were listed as suggested languages. Setting language to Pseudo English immediately caused the launcher to crash repeatedly, as indicated by the popup informing that the "launcher keeps stopping". Swiping up to go to the home screen was now disabled, the navigation gesture bar gone.
In Language settings, English (United States) had now been removed, only the pseudo language was shown. When tapping "Add a language" the screen crashed and I was back in the Languages main screen. I was able to disable Pseudo English by going into the Region screen and switching from Pseudo Accents to United States.
I enabled Pseudo English again to see what happened when I rebooted. The quick settings panel could still be opened and I opened the power menu from there and tapped restart.
Now indeed I didn't get past the GrapheneOS logo. I found out that you need to hold the power button for 30 seconds to force the phone to reboot, has always been 10 seconds on every device I've owned. Very annoying to have to press it this long, especially when having to do it repeatedly during troubleshooting.
Booting into safe mode following Google's instructions (“When the animation starts, press and hold your phone's volume down button.”) didn't work.
I tried to change the active boot slot from the bootloader:
$ fastboot --set-active=other
Setting current slot to 'b' FAILED (remote: 'command (set_active:) is not allowed when locked')
I found a list of fastboot oem commands that exist and tried fastboot oem disable-usb-debugging thinking if you can disable developer options the pseudo language may be deactivated, and maybe this would do that (far stretch but worth a try). It said OKAY but the device still didn't get past the GrapheneOS logo.
I factory reset the device from recovery and all is well (for those that have no user data to recover, that is...)
I found 2 reports of this bug when Ducking pseudo locale hangs phone, one from an Xperia XZ1 user in 2021 (reported on both Stack Exchange and XDA) whose phone booted into an unusable state (but could show a power menu and receive phone calls), and one on the issue tracker of crDroid in 2022, where the result is a bootloop:
https://github.com/crdroidandroid/android_device_xiaomi_vayu/issues/2
A workaround is described for phones that have a recovery that allows you to access and overwrite /data/system/users/0/settings_system.xml and replace all occurrences of en-XA (or ar-XB) in the file with e.g. en-US.
Someone there comments saying the issue is that all strings are converted to the pseudo language, even for example in intents sent by applications, resulting in bogus intents.
The person reporting the issue remarks:
“This is weird. The absence of this tool restricts developers from properly testing their applications.”
Nevertheless, here we are four years later...
It also seems unlikely that a software as big as the stock android settings would have such a severe bug.
Welcome to Android. Have you heard of the bug that enabled anyone to bypass the lock screen of an Android device some years ago? It existed for a while before someone found it, and even longer before Google fixed it (if I recall correctly they didn't even treat it as super severe). This bug that bricks your device? They may not care about it at all, if they even know about it.
I may not setup my phone for a while, so if there's anything I can test to help, let me know.