Confusing behavior when switching admin interface language

I assume I'm doing something wrong but can't figure out what it is.

I've switched my admin user language to German (same issue for several non-English languages I've tried though):
and click Save, but the language of the admin interface remains in English.

I've confirmed that under `user/accounts/[user-name].yaml` I have the line
`language: de`

I only have one user and am on my local machine.
I'm on Grav v1.7.33 - Admin v1.10.33.1.
I've tried clearing my cache.
I tried flipping the Config>System>Languages>Translations to "No" and got the plugin to be in "no language" (just variable names), but when I flip it back, it's back in English. I also tried toggling the "Translations fallback" parameter but that didn't seem to do anything.

Any ideas what could be causing this?