Log in screen use non default browser language

If I open Business Central with "Accept-Language:en-US,en;q=0.8,cs;q=0.6,ru;q=0.4" HTTP headers (English as default, than Czech, than Russian) Log In screen will be shown in Russian (Czech is not supported, but not in English?). After log in Business Central will use "locale=default" (English localization).

If your browser use Russian (or any other supported language) as default browser language both of log in screen and entire Business Central will be opened in Russian (or any other supported language).