To change the currency of the prices you need to use the HTTP header X-Musement-Currency.

The endpoint GET {{api_base_url}}/currencies returns the full list of supported currencies. The supported currencies follow the ISO_4217 standard.

Example
Get prices for an activity in British Pound GBP

curl -X GET \
  '{{api_base_url}}/activities/0f54ca01-2046-11e7-9cc9-06a7e332783f'
  -H 'X-Musement-Currency: GBP'

The response will contain

[...]
"retail_price": {
    "currency": "GBP",
    "value": 24,
    "formatted_value": "£ 24.00"
}
[...]