Cannot go back to system-defualt language properly

[skull591]

Bug description:

When using the app, I accidentally changed the language. So I tried to change it back by selecting the System Default in the language settings. However, it doesn't work and the language stays unchanged.

To reproduce:

1. Go to the settings page and select any language
2. Go to the settings page again and select System Default

App version: v5.7 downloaded from F-droid.