segfault authored Jul 20, 2020 and intrigeri committed Jul 21, 2020

I see that this is not super obvious, but KeyboardSettingUI.apply()
assumes that the keyboard setting was changed by the user, so it sets
IS_DEFAULT (which is somewhat misnamed, it should rather be
WAS_SET_AUTOMATICALLY (or WAS_SET_BY_USER, with the opposite value))
to false.

When the keyboard layout is changed automatically because the language
was changed, we want to set IS_DEFAULT to true, so we don't call
KeyboardSettingUI.apply(), but directly self._setting.save().

What was missing was the call to apply_layout_to_current_screen(), which
was causing #17794.