Take the currency from the amount and not from the locale

How to do it

A Swede browsing in English must still see the 129 SEK you will charge, not $129. Keep each amount and its ISO 4217 code together, as Hold money as integer minor units everywhere says. Pass that code to the formatter every time. Never read a default currency from the locale or the browser. Convert minor units with the currency's own number of decimals, as money explains. Prices in several currencies follow Set a price in each currency.

Examples

JavaScript example

const MINOR_UNITS = { SEK: 2, JPY: 0, EUR: 2 };
export function formatPrice({ amountMinor, currency }, locale) {
  const amount = amountMinor / 10 ** MINOR_UNITS[currency];
  return new Intl.NumberFormat(locale, { style: 'currency', currency }).format(amount);
}
formatPrice({ amountMinor: 12900, currency: 'SEK' }, 'en-US'); // "SEK 129.00"

Python example

from decimal import Decimal
from babel.numbers import format_currency, get_currency_precision

def format_price(amount_minor: int, currency: str, locale: str) -> str:
    amount = Decimal(amount_minor).scaleb(-get_currency_precision(currency))
    return format_currency(amount, currency, locale=locale)

format_price(12900, "SEK", "de_DE")  # "129,00 SEK"

How to check

A test renders the cart, the checkout and the receipt for a SEK order in the en-US, de-DE and ja-JP locales. Every amount shows SEK and the charged number. A search finds no currency formatter call without an explicit currency.

Sources

• ECMA-402 (NumberFormat objects, currency option)

Related rules

• PAY-10 Hold money as integer minor units everywhere in Payments and billing
• API-8 Send money as an integer with its currency in API design
• PAY-66 Set a price in each currency instead of converting at checkout in Payments and billing