Pls use the pot files in ‘invent/languages’ folder as a template to create .po files.http://www.poedit.net/ -Poedit is the popular free editor for creating .po and the corresponding binary .mo files.
You may need to do an update in POEdit to see all the strings.
I don’t think you understood my question at all. This isn’t a language translation. Both of those words are english. I’m asking how we change the word course to lesson in the theme. Not all schools use the word course and ours wants to change it to lessons.
Translation is a good way to go about this if you do not want to modify the source code and maintain compatibility with latest version of the theme. You just use en_US.po file to translate (in your case, that amounts to renaming since the language is the same) the strings.
If you need to modify the source code and change the strings manually, you can have a look at the line number 103 to 146 of framework/presentation/custom-post-types.php file.