It will be fixed in the next update. I assume you have the MultiSites plugin disabled? The only workaround would be to enable it if you want to see the original translation which is "Site Search" or "Recherche sur le site" in French. You should be able to use the Sites Manager even with the missing translation though.

@mattab we had a similar problem in #6014 . Not sure if we can somehow prevent such issues. Probably only with a lot of effort and given that they occur very rarely, are easy to fix and do not cause any "damage" it might be not worth looking into a solution. On the other side we might use more and more translations in the future as we use more Angular etc. Feel free to open a new issue in case you think it is worth looking into it.