But perhaps this is not in common use amongst native English speakers!
For usages like this, it's usually better to use books.google.com. There, you can find many instances of the phrase "American concern" used to mean "American company" by everyone from official US government sources to journalists to writers.
The usage dates back quite some time, if it was borrowed from the German and not a native English word descended from Old English, it was more than a hundred years ago. It certainly predates the modern German legal definition of a concern.
Here is an English example from 1840: https://www.google.com/books/edition/The_North_American_Revi...
EDIT: This definition is also in Samuel Johnson's 1755 dictionary.