Each wish keeps the currency of the store it came from, so one wishlist can show items in different currencies side by side. Wishpicks shows each item's original price and doesn't convert anything into a single currency.
Why this happens
When you add an item, Wishpicks saves both the amount and the currency from that store. A UK item stays in £, a German one in €, and so on. Nothing gets recalculated into your local money, which is why £, €, and ₴ can sit on the same list.
Your region only sets the default. The country you've chosen decides how prices are formatted and which currency stands in as a fallback, and that fallback only kicks in for an item that has no currency of its own.
What you can change
Currency follows your country. There's no separate currency picker, so to change your default, change your country on the Choose region page.
Changing your country won't re-price anything. Each item keeps the currency it was added with, and a country change only affects formatting and the fallback for items with no currency.
Good to know
Mixed currencies are normal on a shared wishlist where people add items from stores in different countries. Everyone sees each item priced the way its store listed it.