next-intl owns Klaviyo nl-NL email copy

This was a fashion storefront, not a demo inbox

Next.js storefront. Centra as commerce. Klaviyo as the mail pipe. next-intl as the dictionary. The market that paid the bills spoke Dutch. If a receipt arrived in English, the shopper did not file a Jira. They forwarded it to support and asked if they ordered from the wrong site.

What they would notice if it failed

Order confirmation in en. Password reset in en. Shipping update that says "Your order" to a profile whose Centra language is nl-NL. Klaviyo still "sent." The metric still fired. The copy was just from the wrong room.

The puzzle: Klaviyo is not a locale

I treated Klaviyo like it would pick Dutch because the profile had a Dutch email and a Dutch shipping address. Klaviyo sends whatever string you put on the event or in the template. It does not run next-intl. It does not read your Next.js request locale. A flow triggered off Placed Order will happily render the default template language.

The storefront already had next-intl wired for nl-NL. Product pages were fine. Transactional copy lived in a second pile: hardcoded English in the Klaviyo template, or a server helper that called getTranslations() without a locale and inherited the default.

That default was English. Of course it was.

Resolve nl-NL before the event leaves

Transactional HTML that we still render ourselves goes through next-intl with an explicit locale. Not "whatever the current request is." A Klaviyo event can be sent from a webhook, a queue, a Centra plugin callback. There is no incoming Accept-Language. If you do not pass nl-NL, you get the default.

const locale = profile.language === 'nl' ? 'nl-NL' : 'en';
const t = await getTranslations({ locale, namespace: 'Transactional' });
 
await klaviyo.events.create({
	data: {
		type: 'event',
		attributes: {
			metric: { data: { type: 'metric', attributes: { name: 'Placed Order' } } },
			profile: { data: { type: 'profile', attributes: { email } } },
			properties: {
				subject: t('orderReceipt.subject'),
				preview: t('orderReceipt.preview'),
			},
		},
	},
});

When Klaviyo owns the template, the template must branch on the profile language Centra already syncs (person|lookup:"Language"), or we send pre-rendered next-intl strings as event properties. Guessing from the shipping country is how Belgium gets French and the Netherlands gets English on a Tuesday.

next-intl already knew nl-NL. I just had not invited it to the email.

Happy coding!
Sander