The story you may have heardTwo stories are often repeated. One, still on Wikipedia, takes scarlet from Persian saqirlāt; but Persian forms appear only in the 1290s, a century after French escarlate, and are themselves from Arabic. The other, in Etymonline, makes it Germanic 'shorn cloth' (scar + lachen); but German Scharlach got its -lach by reshaping, so it shows a Germanic remodelling, not a Germanic source. The Arabic siqillāṭ route is the best-supported account, not a proven one.