As a Mediawiki sysop, you are allowed (per default) to delete translations pages created with the extension:translate (like for any other page). Unfortunately, one time you have done this, you are neither able to view the deleted translation nor to restore it. Mediawiki complains with the following message:

Permission error You do not have permission to view this page's deleted history, for the following reason: The action you have requested is limited to users in the group: Administrators.

After asking, it has been told to me that this was not a supported use-case:
https://www.mediawiki.org/w/index.php?title=Extension_talk:Translate&offset=20150407060756&lqt_mustshow=55715#Unable_to_undelete_as_sysop_55694

IMO, it should, because for now, from a user perspective, deleted translations simply vanish for ever. A way should be provided to restore them.

Remark: done with MW 1.24.1 and MLEB 2015-02