Figure out if update.php can be run in another language

[klonos]

This came up in #5092:

@findlabnet

The language prefix (in my case "en") has been removed from the URL, so the update is done in the default language, not English, and 404 is not returned.
Not perfect, but it works.
...
Don't get me wrong, please. The fix is done.
But switching me to a language that may not be so familiar to me makes me wonder if I may have done something wrong.

@indigoxela

I wouldn't know how to avoid it, ... point us to a D7 patch that fixes it - honestly, I doubt there is any.

@laryn

Would it be worth displaying an informational message indicating you've been switched to the default language to run the update?

@klonos

I've searched to find any follow-up issue in drupal.org to make update.php work in multilingual situations, but I couldn't find any. It seems that our Drupal brethren may have accepted that as an architectural fact ("works as designed") 🤷🏼

[klonos]

/core/update.php seems like a similar situation as /core/install.php. How do we achieve multilingual in the installer? Can it not be applied to update.php as well?