Is trading in foreign currencies through the "margin" system permissible (halal) or forbidden (haram), especially with the presence of "spread" as a difference between buying and selling prices, and commissions from brokerage firms?

The questioner did not clarify how the rest of the deal is covered, but it is likely done through a loan from the company, which is forbidden whether it is with or without interest (riba). As for the spread, it is not used for coverage. The purchase of currencies at exchange offices is done by paying the full price, and it is permissible to buy and sell currencies provided that the full price is paid and immediate possession is taken. The company's commission is permissible if the work being intermediated is Islamically permissible, and if it does not lead to any forbidden Islamic matter, such as the company lending money to the client to obtain the commission, because that is a loan that draws a benefit, which is forbidden. The broker's fee and the work being intermediated must be known, and the broker is an agent who is not liable unless there is transgression or negligence.