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Note: The module may contain language files. If so then just leave them in the folder and they'll be found automatically. However, language strings cannot be edited using the Site Administration > Language editing interface.
This is different from earlier versions of Moodle (I'm upgrading from a pre-UTF-8 version), where the language files had to be moved to the main language folder. What I am wondering is how to handle strings that pertain to these contributed modules in custom language packs. For example, I use the book module but I refer to certain parts of the book module differently in different courses. Do I still put these strings in a file in the relevant custom language pack in the moodledata folder?
The documentation seems to be obsoleted. It is possible to customize strings in contributed modules using the standard translation tool. These add-ons appear at the buttom of the file selection list - see the attached screenshot.
So am I correct in understanding the modified groupselect.php language file location would be?