How would you feel about coming with instead of Marty?

This is very similar to this one.

Maybe check the Midwest and North Central dialect links to see if you find other similarities to German.
https://en.wikipedia.org/wiki/Midland_American_English

https://en.wikipedia.org/wiki/North-Central_American_English

I’m not sure if you know that German is the most common ancestry in the US. The Midwest and North Central US have the heaviest concentration of German ancestry. In parts of North Central you can even hear what sounds like a Germanic accent.

If you look at immigration patterns over the decades, there trends with countries of origin that often coincide with something going on in those countries. In the early-mid 1800s there were large numbers of Irish immigrants. (The Great Potato Famine in Ireland.) This overlaps with a large number of German immigrants in the mid 1800s. If I’m not mistaken there was a lot of war going on in central Europe at that time.

The immigrants commonly ended up in the regions of the US that happened to be growing at the time. The Mid-1800s were approximately around the time of statehood in the north central US.

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