I have the latest version 5.1.1 of civicrm. A problem that kind of slipped past our organization in the past is that the page for opting out has been always in English. Mostly people opted out still without a problem, because I guess most Slovaks know enough English to handle that sort of thing, but there would be occasional emails from people asking to unsubscribe that my boss/wife would get complaining about the opt-out process.
I though I had fixed it through setting CiviCRM to follow the Drupal language, which defaulted to Slovak unless I was logged in. Now I realize that just fixed everything but the text of the opt-out page. So I've just changed default language of civicrm to be only Slovak and never change, and for good measure, set Drupal to just be in Slovak. (I can handle it after 8 years of living in Slovakia and learning the language!).
The link for optout sent was: https://info.cbreurope.sk/sk/civicrm/mailing/optout?reset=1&jid=somenumber&qid=somenumber&h=somenumber
What am I missing? BTW, we are using the Mosaico plug in for sending emails. Could that be a problem? Drush is running the cron jobs.