Why Steam shows a certain currency, when the store country changes, and what it means for gift cards.
Steam uses your store country to decide prices and the currency of your Steam Wallet. The wallet currency is normally set the first time you add funds or buy something.
Steam updates the store country based on where you live and pay. If you really move, Steam may ask you to confirm the change with a purchase using a payment method from the new country.
If you travel for a short time, you do not need to change anything. Your wallet and store stay as they are.
Check your wallet currency on Steam under Account details before buying a large card.