CiviMail opt out language
The Slovak translation of CiviCRM is only 16% complete - so it's not surprising that some pages wouldn't be translated.  This template (templates/CRM/Mailing/Form/Optout.tpl) is correctly configured to be translated, so it seems that this is simply a case of untranslated strings.

If you or someone you know would like to improve the state of the Slovak translation, consider registering for a Transifex account.  You'll have the opportunity to enter translations for various English text, which will automatically be added to the Slovak translation files, which you can then download to your site.  You'll also be helping other Slovak-speaking organizations with your efforts!