Hello.

How to change "Read more..." to my language?

www.new.ekopartner.org.pl/

You need to install K2's Polish language pack.
Your site's language should be in Polish as well too.

getk2.org/extend/translations

OK.
I installed polish language pack, but I still have "Read more.." not "Czytaj dalej..."

Please see www.new.ekopartner.org.pl/ -> EKO Wiadomości module

Then it is hardcoded in your template.
You can compare your overrides with K2's default template (category_item.php., user.php, tag.php and latest_item.php) and place the original language string where it was stripped from.

This post will help you.
getk2.org/documentation/tutorials/174-templating-with-k2-and-the-concepts-of-sub-templates

Thanks. I change it in my template files. thanks.

You 're welcome Michał