Thanks, Ralf, this is a very good explanation.
These packages were created to be used with the Moodle Workplace product. English pack (en_wp) will contain customisations of the core/standard plugins language strings to make them better suitable for the work environment. Workplace language packs in other languages (**_wp) will do the same and also contain translations for the plugins used in Moodle Workplace.
Only Moodle Partners that are involved in development and hosting of the Moodle Workplace will be maintainers of the workplace language packs (except for English that is maintained by HQ). As with any other language pack they can accept suggestions from the community. However, Moodle Workplace code is not available for download and translations that are done without seeing the product may be inaccurate.