(Reply to 2 bad links in Gmail plasmoid for images )
We do exactly what you suggest with new pages being written. However this is an old page and is already in the translation system. We could add a warning at the top of the page, but the page would still be in the translation system and would still show up in the translation statistics. I'll try to investigate a bit more over the weekend and see if I can come up with something better.
Identifying old pages that shouldn't be translated is a major undertaking and we lack the manpower. Currently we simply deal with pages one at a time as they are reported.