I tried following the meson instructions in the `README` (what read the instructions??) and it works!!! rocket
For me plugins configures, compiles and add-ons works!!! (only one that I use :-) with `./autogen.sh --prefix=/home/lex/geany-meson --with-geany-libdir=/home/lex/geany-meson/lib/x86_64-linux-gnu`.
Oh, I didn't try this yet and yes, it seems to be the trick (and pretty obvious after Lex has revealed it :D). Sorry for not seeing this myself.
@kugel- when you are at @elextr's README suggestion, there are also two minor README code comments open which you could you check?
Apart from that, I would like to agree with Lex: seems good to go and thanks for your efforts and patience!