It's like an invisible fire field; you suffer from radiations circa 15-20 HP/square you walk (in Power Armour). Green fumes particle effects are associated with it, the same as those used to mark a location on the Fuel Deposit map, but you don't have to walk through them. I play on v2.5, and you sure have played such a crash-landed Gunship map, did you? However, the only way to read this sentence is to walk close enough to an engine (or a separated engine). If you use to win those maps ever before one of your soldiers comes close, it's no wonder you never notice it.
Anyway as it appears in English, I wanted to know whether the string lies in the map file or in the source code. And if it could be made translatable. I'd bet there's the same localization problem with the new mission objectives, but I don't play v2.6. I hope I can play the Fuel Deposit map soon again.
Secondly, the Medikit section could be complemented so as to briefly mention that it can't treat radiation sickness effects on the spot, besides the use of painkillers.