European blades are made with a different design/process, requiring the edge to be hardened by hitting with a hammer.
Blades from Britain and the USA are made differently and peening / hitting British origin blades will ruin them.
British scythes rely on having a fairly rough edge to the cutting blade, a little like a very fine serrated knife in miniature, which cuts the weeds/grass a bit like a saw, hence sweeping the blade along in a saw like action against the grass.
European blades rely on being smooth sharp and cut more in the style of a razor blade, relying on a smooth blade.
I seem to remember when I researched this, it was thought to be something to do with not only technological approaches to blade making, but also about the conditions scythes were used in. British scythes cope with damp material better. Summer on the continent is apparently historically drier, so there is less moisture to be found among leaves etc. UK traditional blades are also more practical to sharpen in the field and you can just take a stone with you and you do not need hammers/striking surfaces.
If you go to an old fashioned iron mongers (they do still exist) or to a farm suppliers, now known as 'country stores' (they vary from region to region but 'Mole Valley Farmers' is one) you may find a traditional 'cigar' shaped sharpening stone, thought a bit less common than they were. I got a couple of spare stones from various iron mongers this year - try country town ones rather than city ironmongers.
Such 'stones' are of a course grey grit material, about a foot long and are cylindrical. They are usually hung on display in card backed packets with a clear plastic front. They are fatter in the middle and taper towards the ends. This tapering angle is to help you sharpen things at the correct cutting angle. The stones are brittle, so do not drop them. They should be moistened with water, not oil.
You may also come across a finer stone, very similar to the cylindrical cigar stone, but thin and flat rather than totally round. They also have a cigar shaped profile. You can hold these in the same way - with the shaped taper against the blade. They are less traditional, but will do if you cant find the traditional ones. I have used both designs for sharpening bill hooks, grass hooks (heavy blade flat to handle), hand sythes (lighter blade, set at a cranked angle) etc. I find a grass hook a very handy thing for clearing small bits of garden etc. You can also get smaller garden sythes with a blade about a foot long usually on a tubular metal waist high handle/shaft, its for small areas and you do not need to get down nearer ground level, as you do with a grass hook. I love my grass hook though as it is a hand held tool with a very robust blade, it was apparently often used for clearing ditches etc rather than fine work and cuts well through brambles etc.
Both sharpening stone types will be around £5 to £8 approx. I like to keep a spare, just in case one fractures. You can shapren with just a 'bit' but I dont like my hand to be too close to any blade I am making sharper, so would advise not using a broken stone in the field if avoildable as its nice to have fingers.
Try your local wildlife trust, they often run scything classes, sometimes for free, in the summer months - it is most often then as the grass is a good length and they have land they want to clear at that time.
Keep pets and kids well clear, its not very easy to stop a swinging blade once its in motion and all of the above are very sharp. Kids and pets with legs and faces are also nice things to have!
PS
Always carry your blades covered (in something it cannot pierce easily) or at the very least facing so that if you trip or anyone you are near trips, you will not fall on to the blade or endanger anyone else with it. This also applies if resting it against anything etc.
There is no need to fear sharp blades, but every need to be conscious all the time about where the blade is and how if something goes wrong, it might intereact with you/kids/pets.
