The Foreign Exchange market (Forex) is the world’s center for exchanging currencies.
That is if by "foreign exchange" OP means forex and not some crypto exchange registered in a foreign country.
Of course, these markets are connected, just like crypto exchanges and stock exchanges. If the value of a foreign currency goes down and that currency can be exchanged for BTC, one can buy less of that given fiat for the same amount of BTC. At some point if the difference in value is greatly in favour of BTC people may take it as an opportunity and start buying cheaper fiat.