Language

Prices and the checkout's texts are in ?lang= (URL parameters), else nextConfig.locale, else the campaign's language. nextConfig.translations replaces any text by its key. Set both before the loader script.

CODE

<script>
  window.nextConfig = {
    locale: 'fr-FR',
    translations: {
      fr: { 'fields.postcode.errors.blank': 'Il nous faut votre code postal' },
    },
  };
</script>

A text comes from the page's translations (fr-FR, then fr), then the address service, then English. Every key, its default in each language and how to override it: Languages.

Text	Key
A field's message	`fields.<field>.errors.<error>`
City, state and postcode	`fields.<field>.label`; other labels the page writes with data-next-i18n
Card fields	`payment.card.*`
A declined payment	`payment.errors.<code>`, else `payment.errors.generic` (Payment errors)