Is the questioner obligated to return the capital, or part of it, or the commissions that the company deducted from the capital owner's account for his benefit, after the loss of the money in trading international currencies, despite their agreement?

The described transaction is called Mudarabah (profit-sharing) or Qirad, and it is permissible if its conditions are met. One of its conditions is that the profit must be specified as an undivided share. It is not permissible for the capital provider or the worker to stipulate a fixed amount for himself. This Mudarabah is invalid because it stipulates a commission deducted from the capital provider's account for the worker, and because it combines the meaning of Ju'alah (fixed fee) and Mudarabah, which is impermissible. When Mudarabah is invalid, the profit and loss belong to the capital provider, and the worker is entitled to an equivalent wage (ajr al-mithl) if there was no negligence on his part.