@Lia No problem :) Wish I could have been a bit more detailed or precise in the response but hard to not risk being misleading when the original question doesn't include all context.

Never use t() for variables, it's only meant for string literals. drupal.org/docs/7/api/localization-api/… If you want to translate node titles, use a module designed for that. Likely one which relies on the i18n module package.

You can make it an admin path by toggling the "Use the administration theme when editing or creating content" option under "Appearance". That makes all routes with the option _node_operation_route enabled also get the option _admin_route. \Drupal::service('router.admin_context')->isAdminRoute() checks that flag for the current route by default.

Also highly unlikely Drupal actually modified your all your data at once, especially if there was nothing in the logs about it. How are you looking at the database tables? Using a tool like phpMyAdmin? Could it simply be that the font has changed and the one being used does not have those characters?

It's worth noting that since the colors are added using inline styles, they will be removed by Drupal's XSS filters if the text format has "Limit allowed HTML tags and correct faulty HTML" enabled.