This is a fabulous site about Billhooks~
https://www.billhooks.co.uk/. (I hope it's OK to link..).
An incredible collection & amount of information.
Most of my stuff is in storage right now but I've found images of some of them.
The first three images are of an old English Elwell blade I found and re handled, centre is Elwell's catalogue image. Just about every region/county in England had it's own shape of Billhook at one time, pattern's usually named after the county, the same with hammers.
Fourth & fifth image is a Portuguese style billhook that same as Fernando has shown already, many variations like it are typical of the Alentejo region, this one was used for grape vines.
Sixth images is a French Leborgne (& Elwell again), similar to Sajen's image above, I've also seen them branded Rinaldi, which I believe is Italian.