That helps. Now, let's look at options for fixing this thing, I see two possibilities.
The tang is too thin, nothing you can really do about that. But, on a knife that small it won't matter much if you use a strong handle material and bolt it together (not pins). If you use something like Micarta for the handle the handle slabs will be strong enough and stiff enough to reinforce the weak tang. You will need to use bolts to secure the handle, Loveless bolts are the usual item for this. They basically consist of a long screw with two round nuts, one nut on each side of the handle and the screw pulls the handle down tight. Very strong. Pins are simpler but they won't hold the handle together if the tang tries to flex. You need to find a knife supply place in your area or order from the USA to get these parts. Or, once you look them up on the internet and see how they work you can probably make something similar yourself.
The second way would be to cut the tang down and make a stub tang handle. All that means is your tang would be about 5cm long and narrow. You would need to make a ferrule for it, in this case that's nothing but a flat piece of metal with a slot in it that will fit over the tang. The handle would be one solid piece of material (probably wood). You put a hole in one end of the handle, the tang goes in the hole, and then a single pin can be used to secure the handle. You can read a more complete description of the process at
http://www.rayrogers.com/stubtang.htm
Since the blade came from Denmark it may be intended as a puuko style knife. Most of them are made in the stubtang style. That may be why the maker let the tang get so thin ...