Default sort (a magic word in wikitext), allows to propose an alternative title to be used when sorting the article. In Visual Editor users can edit this information at the bottom of the Categories dialog, as shown below:

Content Translation currently ignores such information. It is not transferred to the translation, and the user has no control to add it. Users need to make a follow-up edit to the publish translation to add this with a regular editor (visual or wikitext). We may want to explore how to surface such information in Content Translation in a way that (a) allows to transfer and adapt to the translation and (b) does not leak into the translation when it's not intended.

This was suggested by a translator in this comment.