kamiel79

WordPress has the function wp_localize_scripts for translation, but the strings passed to it have to be hard-coded. Until you parse the .js-files and scan for occurrences of _e() with a fast regexp, and localize them with the data using the WordPress _e-function to localize from a .po file. *Note*. Your po-file has to include strings from javascript files. To do this in Poedit, see http://stackoverflow.com/questions/16557327/how-to-generate-po-file-from-js-file-using-poedit.

Localize js

Provide translation function _e("") in javascript files.

Andrei Lupu

Radu Constantin

Translation Tester is a plugin that helps you check the POT file of the theme or plugins from your website. If you want to make sure that all the strings are included in the POT file, you need to create the PO/MO files from it and translate each string, one by one.
This plugin is made to do a simple thing: get all the strings from your POT file and the translated part will be a concatenation between the original string and a prefix at your choice.
The options from Tools -> Translation check help you with uploading and choosing a prefix. Once you press Test button, a PO file will be downloaded to your computer. Just generate the MO file from it, copy both of them in your website and see how it goes.

Translation Tester

Translation Tester is a plugin made to help you check the POT file

Localize js vs Translation Tester