Hello
*TL;DR* Two translations missing on that group https://translatewiki.net/w/i.php?title=Special:Translate&group=ext-thanks&language=en&filter=%21translated&action=translate of messages, three in this group https://translatewiki.net/w/i.php?title=Special:Translate&group=ext-echo&language=en&filter=%21translated&action=translate . Links are set on English, don't forget to switch to your language; you may have more messages missing depending on your language.
*Details* Presentation models for eight extensions who deal with notifications are going to be changed in a near future: https://phabricator.wikimedia.org/T116834
The five missing translations are the first: https://phabricator.wikimedia.org/T117966
That explains why you may have seen some messages in English on the notifications panel on your wiki. We are going to communicate earlier on these changes, in order to avoid this kind of problem.
Sorry for the inconvenience, and thanks a lot for your help! :)
Benoît