The Romans, on the other hand, couldn't give a damn about the language issue as long as the local tax farmers kept them cards and letters rollin' in ...

Yes, ironically, Latin survived in the various Romance languages in most parts of the western half of the empire. Norman held sway in court for a century or so, and then stuck it out in the law courts until the 17th century or so.

I always thought that the Normans ensured that Norman would be used by importing a newish top-down management from the continent.