'is-active' class is not set in Language switcher for non-default language

@Nor4a, Thank you for reporting this problem. We rely on issue reports like this to improve Drupal core.

I tested this on 10.1, standard install, with Italian as the second language and was not able to reproduce this error. I followed the steps given in the Issue Summary. With Italian as the default language, the language switcher always has one link with 'is-active'.

Therefore, closing as outdated. If you are experiencing this problem on a supported version of Drupal reopen the issue, by setting the status to 'Active', and provide complete steps to reproduce the issue → (starting from "Install Drupal core").

Thanks!