strange - we have two unrelated questions in one thread...

about the seat belt - chances are that the seat belt buckle in the passenger seat is malfunctioning... it was a known issue in E39 and some E34s...

start with simple things first - check fuse F44 in glove compartment. if the fuse is ok (test with multimeter, or replace outright with a 5A fuse), then the issue could be in the buckle itself... i think part # 72119119540... if you are DIY type guy, you may want to check plug X279 under the passenger seat, and short pins 5 and 7.

DO NOT DISCONNECT CONNECTOR X279 (Yellow connector under the seat). try to locate the pins 5 and 7 without disconnecting the connector - if you disconnect the connector, you will light up the airbag symbol in the cluster and deactivate the passenger airbag.

Another option, try to see if the passenger buckle can be taken apart, as there could be a mechanical issue that you might be able to resolve - when the belt is buckled, the belt's blade closes the contact that tells the computer to shut up.

another option yet, program out the passenger seat belt notification, but remember, even if the passenger is buckled up, the force of the airbag will be reduced, as the system thinks that the belt is not fastened...

now, about the headlight issue -

the UK headlights have the metal cutout designed for the right-hand drive and have a manual switch for the UK cars to operate in the rest of Europe, the "continental" mode... the part numbers are obviously different, as the regular euro lights do not have the option for the UK cut-out... you should be able to use the UK headlight in europe, with the cutout permanently switched to the continental mode... i think, the continental mode makes the cutout flat, as opposed to a "step"...

and you should have started a new thread about the headlight, instead of highjacking the seatbelt thread...