FAR/JAR 25
So long as the twin turbine is FAR/JAR 25 certified, you'll be OK (if you want to log multi-crew time). Beware of these programmes that promise PIC in single pilot aircraft (and put you right seat), JAA won't accept those hours.
I got my FAA licenses in the US and am hour building in a multi-crew aircraft whilst studying for my ATPLs. When I return to Europe shall then convert to JAA. You can read Lasors to find out about conversion requirements.