Think about it like this. The average visitor to your site is going to speak Slovak, right? If you link to a page in English, or Russian, or Urdu, or whatever, the search engines have to make a judgment call about the likelihood that a visitor to your page will find that linked page valuable. My guess is that they would value a link to a page written in a similar language or English more than a link to a page written in a very different language because the average visitor to your site speaks Slovak, probably has some knowledge of related languages, and might also be able to read English, but they probably aren't able to read Kazakh or Spanish.

The reason I say that is that Google knows that my site, for example, is written in English, but that I talk a lot about French and German, so there's a good chance that people that visit my site have at least a passing knowledge of those languages, so if I write a blog post about a new German movie and then link to a review of it in German, I would guess that that link would pass more equity than if I linked to a review in Chinese because a link to a Chinese review holds no value for my average visitor.