German makers first devised crooks to make such horns playable in different keys—so musicians came to use "French" and "German" to distinguish the simple hunting horn from the newer horn with crooks, which in England was also called by the Italian name corno cromatico (chromatic horn).
Furthermore, when did the French horn originate?
While it is true that some of the horn's history originated in France, it is far from its exclusive heritage. Actually, in France it's know as the horn ("cor") or German horn, and in Germany it's called the hunting horn. In fact, it's only called the French horn by the English.
Why do they call it the French horn?
an alto woodwind instrument of the oboe family, having a bulbous bell and sounding a fifth lower than the oboe. it is called a french horn because it is in the key of f and people misunderstood why it was called a f horn and thought it was f, for french. the french horn originates from Germany, in the key of F.