LPGTech (the manufacturer) puts different firmware onto ECU's for different countries - If you have an ECU that wasn't destined for the UK, the software won't allow you to use English. The part of the firmware that affects this isn't updated when you upload new firmware (so perhaps it is the boot loader or something). So, if you select English in the software but the software reverts back to Polish, you have an ECU that wasn't supposed to be destined for the UK, one that wasn't sold in the UK by the official importer, grey import, and you are stuck with Polish.
Chances are that the calibration is wrong... usually I would say rich (since misfires) and that might be the case here. Autocal doesn't do much really, just guestimates shape of the multiplier line based on injectors set in software and shifts that full line up or down based on correct level for idle conditions. But, the Beemer most likely has atmosphere referenced petrol pressure, leading to low petrol injector pulse duration at idle (due to higher than normal petrol pressure), so multiplier at idle needs to be high, and multiplier high at idle will mean autocal will set multiplier high at heavy loads too. A pseudo fix for this would be to manually adjust the multiplier to be leaner at heavy loads, pseudo because this doesn't address the fact that a given petrol injector pulse duration can inject different amounts of fuel at different manifold pressures due to the fixed petrol pressure but the LPG system won't be set to account for that difference because it assumes petrol pressure is referenced to manifold pressure like LPG pressure is. I set the LPG ECU to correct for this aspect when I convert relevant engines but it won't be possible with LPGTech... nevertheless LPGTech is no more disadvantaged in this respect than most LPG ECU's and very good results should be possible (as they are with other LPG ECUs).
Most LPGtech fitters use Tech mode, which like I implied above doesn't do a great job of calibration - but perhaps in this case it might have done a better job that the installer! I have sorted a lot of LPGTech systems, both modes, but I reckon most of the vehicles I put right with LPGTech using 'standard mode', with software locked to Polish, will have been fitted by the same installer.
Although... another common problem with BMWs is brought about by people fitting incorrect MAF sensors, they can look very similar between BMWs but have a different spec, I doubt this will be the problem in your case but worth mentioning. Also, cam sensor issues are fairly common on them.. sometimes not affecting petrol running much but affecting LPG running more. Any latent codes for cam sensors? LPGTech can connect to a cam sensor to pickup rpm, which could also mess up cam signal if done wrong.
You might be able to get round some of the language issues using a second copy of the software alongside to translate what your seeing on the screen then. IE run it on another machine, or in a VM
Lol no I've tried that and as soon as you connect to the ecu it switches back to Polish
The original installer was I believe Polish (he used his name to set up the map etc) and if so I suspect that it was to ensure returning business (not happening)
BTW the install is over 4 years old so not a recent one or covered by any warranty
More likely given what Simons said that its come over from Poland in the back of a Van or similar. Doubt its anything done to particularly lock you out of going elsewhere, theres a lot of Polish Gas Convertors about (or has been), hardly surprising as its more common over there than here to find LPG fueled cars, Plus some of the kit (lpgtech and KME, plus most of the tanks) are made there too.