You may try what I suggest in the long distance patch thread: add "dialog_tool=,~" in menuconf.tab.
Then you will be able to change to JIT2, but you may run into the same bugs as I did.
I have managed to find a reproducible bug. Look at https://uran.webstep.net/~vladki/simutrans/
, download the autosave07.sve and addons.zip - it is my savegame converted to jit2 - run it with pak128.Britain 1.14 (last single-height stable) and some recent nightly.
It will be loaded close to two stell mills, one wil be quickly recovering from buggy undersupply (demand -200 or so). Then you can watch the steel demanding industries slowly restart production and waiting steel trains to leave the station. When you load the game there are a few trains waiting for cargo, but when the steel is produced at full, at most one train shall be waiting for cargo.
Then let the game running for a while and move to the other end of map - find car dealer in Christminster. Normally it should be selling some 260 cars/month. (max with power boost is 320). It will slowly recover production. But the trains can deliver 60 cars at once, while the input storage of this shop is only 53. So it happens from time to time that the 7 extra cars are thrown away, and deduced from demand. I am not sure if that is the trigger for the bug. If you run the game until august around 20:00 (in game time), the demand buffer of this car dealer gets quickly satisfied by the car factory and drops to -4, never to rise again. There are still some cars on the way, but they are consumed without increasing the demand counter. It drops even more as some of the supplies overcrowd the dealer. On september 3:00 the last delivery happens, and car dealer is not ordering any more.
With fast forward I got the car dealer broken at august between 12:00 and 15:00. Tried 4 times, and always got the bug, maybe with different timing.