Page slug sometimes works sometimes not

I have multilanguage blog site, English version has slug: custom-slug in articles header… When I go into /blog with EN, than I see slug-routes and all works fine.

But when non-English version of article is active, URL not changed:

1. When I change language using langswitcher plugin.
2. When I type /en/ in address bar instead of the current language.

I see folder-based URL, one article has 2 routes. How to make it change into slug with redirect or something?