Hi Anni,
Thanks for writing in! It could be that your x.pot file may have been corrupted when downloading it. You don't have to download it from your site, instead you can download the latest version of X theme from your Envato account, unzip the x.zip file and then you can locate the x.pot file under the following location.
x/framework/lang/x.pot
Then use that file to do your translations and see if that works.
Let us know how it goes.
Thanks!