How is capital withdrawn from a commercial company in light of exchange rate fluctuations? Is it calculated at the old rate, the current rate, or by discounting a percentage of the currency difference? And what if the currency rate improves?

Profit in speculative partnerships (Mudarabah) and companies is only realized after the capital is secured. If the capital is in a specific currency, the determining factor is the exchange rate of that currency on the day of reckoning. Any amount exceeding the original capital is considered profit and is distributed according to the agreement.