UK to East European shower pipe converter
It's very difficult to tell what your existing pipe is like, as there's a shower attached to it. However, I think your problem is that the existing pipe diameter is larger than the UK shower connection? In which case you need a reducing coupler.

Here's an example. But a) your existing pipe may be 1" rather than 22mm; and b) the fitting at the larger diameter end may not be suitable. However, if it were that simple, then your plumber should have been able to do it. So I suspect problem a). I'm sure somewhere must sell imperial to metric reducing couplers, but I haven't looked.

With regards to having an ugly converter sticking out the wall - your other option is to have the converter behind the tiles. This requires either 1) breaking out the tiles, then retiling a small area afterwards; or 2) coming at the wall from the other side (in which case you'd then need to replaster the other side of that wall). I personally did 2 when installing a new shower, as the tiles were installed by the previous owner, so I didn't have any spares, but it had been done recently so I didn't want to retile the whole bathroom. Option 1 shouldn't be too difficult, as you say you have retiled, so you should have access to identical replacement tiles.