What is the ruling on the percentage a broker receives from a foreign company if he mediates on its behalf to secure a contract with a governmental entity, and does the ruling change if the engineer in the governmental entity requests a percentage in exchange for completing the mediation?

There is no religious impediment to receiving a commission for brokering, so long as the transaction does not involve anything forbidden. If the engineer's request for a percentage is a forbidden bribe to assign work to a company without legitimate entitlement, then it is not permissible to pay it; bribery is forbidden, and both requesting it and paying it are prohibited. As for a bribe by which one obtains their right or repels injustice, it is permissible according to the majority of scholars, and the sin in such a case falls upon the one who receives the bribe.