I use the french translation of Discourse and I found some strings that I can’t translate in the customize part of the admin panel.
“Primary email” when you try to register an account with a blacklisted email domain.
“of” when you click on one image in a post with multiple big images to see it in full screen.
“to” and the entire list of periodicity in the insert date menu.
The display of the month is in English in the message sent for the new user of the month.