I've got a German Cosmos with an English (repro) backglass.
Should be worth a fortune don't you think?
A lot of games got trashed in the 70's because of the sometimes poor quality in paint, as well on backglasses as on the outside.
Lot of games got a woodlike kind of "wallpaper" covering the flaking paint on the outside.
I've got two Cosmos games, both backglasses are more then flaky, the paint falls off by looking at them (got two repros now), one is the outside original paint, one side is flaking, the other machine has no painting at all.
Still: nice games to play, it didn't matter to me what the language was on the game, have a Aces High in German and still love to play it, so...for people who enjoy these games it doesn't matter.
Maybe to a newbie it is important, till they discover that the game is the same (produced in Chicago!)