I solved the problem:
1) you need to add a folder “languages” to the plugin directory
2) add line under “Text Domain” (line 9) called “Domain Path: /languages/”
3) now you can generate a new po file with poedit, translate (There are only 25 phrases to translate so that′s rather easy) and save to folder /languages/
4) Maybe you have to delete the new line “Domain Path…”, I wonder why but for me it worked at first only without that, then also with !?
5) Upload all files to server
Hope that helps