Changing user’s language resets the formats (region) by passing `NULL` to `update_region`.
However, updating the region calls `maybe_notify`, whose callback `maybe_notify_finish`
tries to parse the `mnd->target_locale` (the `NULL`), producing a critical:
GLib-CRITICAL **: g_regex_match_full: assertion 'string != NULL' failed
Since updating the language itself already triggers the notification check,
let’s just skip calling `maybe_notify` here in that case.