You have two parts that you need to replace - the tow bar and the hitch mount.
Tow Bar Fixing the tow bar is pretty easy. You just need a piece of steel tubing that is just a little bit larger or smaller in diameter than the existing tubing so that it'll fit like a sleeve - then bolt or rivet them together. If you aren't carrying kids or animals in the trailer, a solid piece of hardwood doweling would also work.
A good hardware store will have tubing repair clamps that could also work (I'd still drill safety pins/rivets in it to make sure that longitudinal forces don't pull it apart):
Alternately, you could replace the tow-bar altogether by getting tubing of the same diameter and asking a local metalshop (autobody shop, metal sculpter) to bend it to the right angle and drill holes in the right places. Some homecenters also have tubing benders that they can let you use to bend the tubing (they have them for bending electrical conduits). Getting a new tow bar made is the most expensive and might overkill but is the strongest of the options.
Hitch Mount: You could recycle your old hitch mount but they are a wear item and it'd be good to use the occasion to replace it. The parts for a new hitch mount are readily available. My trailers use a Sunlite style hitch:
You can also buy parts for a Burley style hitch:
Cost/Safety/Performance: If the rest of your trailer is as beat up as your tow-bar, you might consider just replacing the entire trailer as your tires and axles are most likely also at the end of their lives. Trailers are pretty cheap and you could just buy a new one for 150 eurodollars or if you look at a thrift store or on your country's equivalent of Craiglists, you might find a replacement trailer for less than 50 eurodollars (which is about what the repair would cost).
If you get one with the same wheel size, you can keep your old wheels and tires for spares. You could also easily repurpose your old trailer as a lawn handcart (wheelbarrow).