It seems the logging code for uploading has been rewritten about a month ago, as there appears to be a new "logentry-upload-overwrite" message.
Since then, the message is hardcoded as an automatic edit summary upon uploading a new version of a file.
It hardcoded the message in Dutch since I used Dutch as interface language on Commons. It used to be in English, which it should be since that is the site language.
(Ideally though we probably need a dynamic edit summary for these cases, but that's outside the scope of this bug.)
I didn't check whether the bug is also present for related messages (maybe "logentry-upload-revert" or so).