mcascant Polylang is not really bad. In my opinion, conceptually it was implemented with some complications. On top of that, I've contacted the plugin's owner and he did not express interest in collaboration, so I've deprioritized this direction for now.
I might do some further investigation and build own plugin for multi-lingual support. Overall it should be really simple because WordPress core already offers all the necessary building blocks, so I just need to stack them in the right order.