As you can easily adjust the text of OptiMonk popups, you can add a text of any language of the world.
If your website is multilingual and the domain name stays the same but URL modifies, you need to do the following:
Create the campaign on the language you prefer, then go to Display rules and find the option "Pages -> Current URL" where you need to do two things.
First, click on "+" button, select equals and add URL which indicates the language of the site, i.e. /br , /ru, /hu, etc.
Secondly, click on "+" once again and select "doesn't equals" where you need to add all the URL addressess of other languages of site. This how you can prevent OptiMonk's popup of a given language to appear on site of alternative language. You need to create as many campaign as many lingual is your site and do the settings for all of them.
However, if by selecting different language the domain name of the site modifies as well, please contact us at firstname.lastname@example.org so that we can discuss the possible actions.