Dear Marcin Rawski
I'm sorry. We just finished the days holiday. So can not help you right away.
Please create the folder for your language by duplicate the folder: en-GB in sj_urline template, then edit the name to your language
the next, edit the name of the files in this folder:
eg
prntscr.com/e3vktb
create edit to folder: vn-VN
vn-VN.tpl_sj_urline.ini
vn-VN.tpl_sj_urline.sys.ini
then copy the text: mod_login_me, sign_up, read_more_k2, K2_no_comments ... translate in the file: vn-VN.tpl_sj_urline.ini
Thanks