Each wish keeps the currency of the store it came from, so a single wishlist can show items in different currencies side by side. Wishpicks shows each item's original price and doesn't convert it into one shared currency.
Why this happens
A price is saved in its own currency. When you add an item, Wishpicks stores both the amount and the currency from that store, so a UK item stays in £, a German one in €, and so on. The app then shows each item's stored amount in its own currency; it doesn't recalculate prices into your local money, which is why you may see £, €, and ₴ on the same list. Your region only sets the default — the country you've chosen sets how prices are formatted and which currency is used as a fallback, and that fallback only applies to an item that has no currency of its own.
What you can change
Currency follows your country. There's no separate currency picker. To change which currency Wishpicks uses as your default, change your country on the Choose region page. This won't re-price items that already carry their own currency.
Changing your country won't convert existing prices. Each item keeps the currency it was added with. A country change only changes formatting and the fallback for items with no currency.
Mixed currencies are normal on a shared wishlist where people add items from stores in different countries — everyone sees each item priced as the store listed it.