As a translator I fully agree with this approach! That’s far the better solution to solve the pain to have F-Droid app descriptions in several languages => description will be done by app main translators themselves (it’s like other strings of the app).
This solution,“to add F-droid description in the app project itself”, is part of what I’ve called “an upstream” content (see my post above).
translating apps description is a pain. We must think how to initialize content with “upstreams” (Google Play description …) or we will miss one of our mission: promote FOSS.
For some apps missing this F-droid description in the project, it may be usefull to find an other automated source for F-droid app description (like stated above “Google Play Description” but it can also be the app website).