And loose the id in the title?

I'm inclined to decline or mark this as invalid. At least as a filename this is not possible, if you mean the title= parameter to {{photograph}} then it is possible, but not quite useful. As I understand it all photographs should be manually reviewed for metadata and categorization and using a internationalization for the untitled images (and for no other case) may confuse the process by indicating it is done for that photograph (or that field, at least).

I mean for the 'title' parameter.

Would it imply that? In my view it just makes the cleanup process easier for me as an importer.

In my opinion, in cases where there the photographer has not chosen a title for the photo at 500px the title parameter should be left empty, not set to {{untitled}}, The title field should only be set to {{untitled}} for works of art where the artist has affirmatively asserted his or her work is untitled.