At the time, nobody really cared about the languages and cultures, they cared mostly about regular payment of the taxes. Language become only important, when you had the ambition to get a job at the royal court or somewhere nearby hierarchy-wise. Since the monarchs were getting married across the entire Europe, it was unknown, which language will be the next hip one.

Languages and nations got their prominence only after French revolution, as a new bonding for the statehood, once the monarchs were gone.

If something really wanted to change the customs and culture, it were religions, not empires. Not even Roman Catholics managed that, though.