I think we might want to override this to Project:Books on Wikimedia wikis (otherwise the books clutter the content books category)
Draft step-by-step process to fixing this (started by @Amire80; feel free to correct it):
- Check whether any Wikipedias localized the name using Global Search. (This will be useful for understanding the necessity.)
- Take a look at the category with this name on wikis that use the Collection extension (or at least at a sample of wikis), and understand the extent of the problem.
- If the above steps don't bring up something very weird, add a message to WikimediaMessages that overrides this category.
- If feasible and necessary (according to the first step in this list), add the existing translations without having to go through translating on translatewiki.
- After deployment, check that the new category works as expected.