Not necessarily, note that I wrote, “expressed in existing ways” and not, “spoken/written in existing ways”. Expression itself has a greater breadth than language alone, e.g. movement, drawing/painting, instrumental music arrangements, etc.
It includes language, absolutely, but it is not limited to language, which makes for a more challenging question imo. If not expressed in existing ways, it would meet the criteria of entirely new and unthought of, presumably, but it would also likely fail to be recognized as an expression at all.