It may only be a sticker but the fact it's a sticker isn't the deciding factor. The objective with any record on here is to identify the country of release. The sleeve with the sticker on it was not released in Britain, it was released in Germany. Hence, it's German. Surely?

If an imported record was put into a German-printed sleeve and then released in Germany, we'd agree THAT was German, wouldn't we? This is no different except the sleeve has been localised in a different (and quicker/easier) manner.