Now here is a conundrum! I long thought of Have a Nice Day as an American song but it was not until I auditioned to join a small mixed Bremen group [Christian, Henner, Maja, Marlene] in the early 2000's that I learned otherwise.
The words and music are by Lorenz Maierhofer, an Austrian, and are published in a German language choir book, 4 Voices, published by Edition Helbling. So that, dear surfer, re-classifies this song as German according to definition(s) I have given elsewhere in these webpages.
It is a cheerful. lively piece sprinkled with "doo doo"'s and "dum dum"'s mixed with snapping fingers and rounded off with a good old fashioned "Oh yeah!". It could be American could it not!