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Internationalization (i18n)

Storefront Next uses i18next with remix-i18next to support multiple languages and currencies, with runtime switching that doesn't require a page reload. A server-side instance handles server-side rendering (SSR) with full translation access, while a client-side instance loads translations as static JavaScript chunks, keeping server and client in sync without hydration mismatches.

Prerequisites

  • Node.js 24+ and pnpm installed
  • Project dependencies installed (pnpm install) — i18next and remix-i18next are included
  • At least one translation file at src/locales/[locale]/translations.json (e.g., src/locales/en-GB/translations.json)
  • For extension translations: run pnpm dev or pnpm build once to generate the aggregated files under src/extensions/locales/. These files are auto-generated and must not be edited manually.

Quick Start

React components use the useTranslation hook. Everything else uses the getTranslation function.

For React Components:

import { useTranslation } from "react-i18next";

function MyComponent() {
  const { t } = useTranslation("product");
  return <h1>{t("title")}</h1>;
}

For everything else (loaders, actions, utilities, helpers, tests):

import { getTranslation } from "@salesforce/storefront-next-runtime/i18n";

// Client-side or non-component code
const { t } = getTranslation();
const message = t("product:title");

// Server-side (loaders/actions) - pass the context
export function loader(args: LoaderFunctionArgs) {
  const { t } = getTranslation(args.context);
  return { title: t("product:title") };
}

Architecture Overview

The i18n layer is split between the SDK and the template:

  • SDK (@salesforce/storefront-next-runtime/i18n) — generic infrastructure: middleware factory, context, shared interpolation config
  • SDK (@salesforce/storefront-next-runtime/i18n/client) — browser-only client initialization
  • Template — translations (src/locales/), configuration, type augmentation, root.tsx wiring

We maintain 2 separate instances of i18next:

  1. Server-side instance: Has access to all translations for the entire site
  2. Client-side instance: Dynamically imports translations as static JavaScript chunks

Both instances support dynamic language switching at runtime without page reloads.

Server-side and Client-side Flow

  1. Server-side middleware detects the user locale and initializes i18next
  2. Server has access to all translations from all locales and renders SSR content with translations
  3. Client-side initializes its own i18next instance, reading the language from the HTML lang attribute to prevent hydration mismatches
    • The initI18next() function in root.tsx accepts an optional { language } parameter to ensure consistency between server and client
  4. When a translation is first requested, the client dynamically imports ALL translations for the current language
    • This triggers an HTTP request for a JavaScript chunk (e.g., /assets/locales-en-[hash].js)
    • The chunk is served as a static asset (pre-built, minified, and cached with long-term headers)
    • Much more efficient than an API endpoint: no server processing, CDN-friendly, immutable caching
  5. All namespaces for that language are loaded and cached in memory
  6. Subsequent translation requests use the cached data (no additional requests)
  7. When users switch languages, the client loads the new language's translations dynamically (if not already cached) and updates the UI immediately

File Structure

src/locales/
├── index.ts                # Exports all language resources
├── en-GB/
│   ├── index.ts            # Exports English translations
│   └── translations.json   # All English translations (namespaced)
└── es-MX/
    ├── index.ts            # Exports Spanish translations
    └── translations.json   # All Spanish translations (namespaced)

src/extensions/
├── my-extension/
│   └── locales/
│       ├── en/
│       │   └── translations.json   # Extension translations (English)
│       └── es/
│           └── translations.json   # Extension translations (Spanish)
└── locales/                # Auto-generated (do not edit manually)
    ├── en/
    │   └── index.ts        # Aggregated extension translations
    └── es/
        └── index.ts        # Aggregated extension translations

src/components/
└── locale-switcher/
    └── index.tsx           # Client component for switching languages

src/middlewares/
└── i18next.server.ts       # Thin wrapper around SDK's createI18nMiddleware()

src/routes/
└── action.set-locale.ts    # Server action to persist locale preference

The i18n utilities (getTranslation, getLocale, mockI18nContext, createI18nMiddleware, initI18next) are provided by the SDK and split across two subpaths:

  • @salesforce/storefront-next-runtime/i18n — server-capable APIs (getTranslation, getLocale, mockI18nContext, createI18nMiddleware). Safe to import from server modules, route modules, and components.
  • @salesforce/storefront-next-runtime/i18n/client — browser-only APIs (initI18next). This entry pulls in i18next-browser-languagedetector, which has no Node support, so it must only be imported from client-side code (e.g. inside useEffect in root.tsx). Importing it from a *.server.ts file will fail to bundle and is blocked by the linter (OxLint no-restricted-imports).

They don't live in src/lib/ anymore.

Configuration

Supported Languages and Currencies

Languages and currencies are configured in multiple places that must be kept in sync:

1. config.server.ts - Application-level configuration:

site: {
    locale: 'en-GB',
    currency: 'GBP',
    supportedLocales: [
        {
            id: 'en-GB',
            preferredCurrency: 'GBP',
        },
        {
            id: 'es-MX',
            preferredCurrency: 'MXN',
        },
        // Add more locales here...
    ],
    // Currencies that users can manually select
    supportedCurrencies: ['MXN', 'GBP'],
},
i18n: {
    fallbackLng: 'en-GB',
    supportedLngs: ['es-MX', 'en-GB'], // Your supported languages
}

2. src/middlewares/i18next.server.ts reads supportedLngs and fallbackLng from config automatically — no additional middleware configuration is needed.

⚠️ IMPORTANT: Keep these configurations in sync. Make sure that:

  • The locales in i18n.supportedLngs match the id values in site.supportedLocales (single-site) or across all entries in commerce.sites[]. supportedLocales (multi-site).
  • Each locale in supportedLocales has a preferredCurrency that matches one of the site.supportedCurrencies or site's supportedCurrencies.
  • Each locale in i18n.supportedLngs has a corresponding translation directory under src/locales/.
  • If you add a new language, update both places and create the translation files.

Currency System:

The application supports independent locale and currency switching:

  1. Locale-based currency: Each locale in commerce.sites[].supportedLocales has a preferredCurrency that's used by default.
  2. Manual currency selection: Users can manually select any currency from commerce.sites[].supportedCurrencies, which takes precedence over the locale's preferred currency.
  3. Currency priority: User's manual selection (cookie) → Locale's preferred currency → Site's default currency.

See the Currency Switcher component in src/components/currency-switcher/ for the implementation.

Locale Detection

The middleware automatically detects the user's locale from:

  1. The lng cookie (if previously set)
  2. The Accept-Language HTTP header
  3. Falls back to the configured fallbackLng

Switching Languages and Currencies at Runtime

Language Switching

Users can switch languages dynamically without reloading the page using the LocaleSwitcher component. The language change happens in two steps:

  1. Client-side update: Immediately changes the displayed language using i18next's changeLanguage() method
  2. Server-side persistence: Submits to a server action that sets the lng cookie to persist the preference across page reloads

Using the LocaleSwitcher Component:

The project includes a pre-built LocaleSwitcher component that you can drop into your UI:

import LocaleSwitcher from "@/components/locale-switcher";

export function Footer() {
  return (
    <footer>
      {/* Other footer content */}
      <LocaleSwitcher />
    </footer>
  );
}

Currency Switching

Users can manually select a currency independent of their locale using the CurrencySwitcher component. When a new currency is switched:

  1. Server submits an server action.
  2. Middlewares (client and server) run to update latest currency into context.
  3. updateBasket is called to SCAPI to update currency accordingly.
  4. Loader func will revalidate and update the UI to reflect the selected currency.

Using the CurrencySwitcher Component:

import CurrencySwitcher from "@/components/currency-switcher";
import LocaleSwitcher from "@/components/locale-switcher";

export function Footer() {
  return (
    <footer>
      <div>
        <h3>Language</h3>
        <LocaleSwitcher />
      </div>
      <div>
        <h3>Currency</h3>
        <CurrencySwitcher />
      </div>
    </footer>
  );
}

Key Points:

  • Currency selection is independent of locale
  • Manual currency selection takes precedence over locale's preferred currency
  • The preference persists across locale changes
  • Falls back to locale's preferred currency if no manual selection is made

Building Your Own Language Switcher:

If you need a custom implementation, here's how to implement language switching:

"use client";

import { useTranslation } from "react-i18next";
import { useFetcher } from "react-router";

export function MyLanguageSwitcher() {
  const { i18n } = useTranslation();
  const fetcher = useFetcher();

  const handleLanguageChange = async (newLocale: string) => {
    // Step 1: Change language client-side for immediate UX
    await i18n.changeLanguage(newLocale);

    // Step 2: Persist to server cookie for page reloads
    const formData = new FormData();
    formData.append("locale", newLocale);
    void fetcher.submit(formData, {
      method: "POST",
      action: "/action/set-locale",
    });
  };

  return (
    <select value={i18n.language} onChange={(e) => void handleLanguageChange(e.target.value)}>
      <option value="en">English</option>
      <option value="es">Spanish</option>
    </select>
  );
}

How It Works:

The /action/set-locale server action (located at src/routes/action.set-locale.ts) receives the POST request and sets the lng cookie using the same cookie object that the middleware uses for detection:

import { data, type ActionFunction } from 'react-router';
import { localeCookie } from '@/middlewares/i18next.server';

export const action: ActionFunction = async ({ request }) => {
    const formData = await request.formData();
    const locale = formData.get('locale') as string;

    if (!locale) {
        throw new Response('Locale is required', { status: 400 });
    }

    const cookieHeader = await localeCookie.serialize(locale);

    return data(
        { success: true },
        {
            headers: {
                'Set-Cookie': cookieHeader,
            },
        }
    );
};

Key Points:

  • Language changes are immediate (no page reload required)
  • The preference persists across sessions via the lng cookie
  • All client-side translations are loaded as static assets (one JavaScript chunk per language)
  • Switching languages triggers the dynamic import of the new language's translations if not already loaded

Usage Examples

In React Components

Use the useTranslation hook from react-i18next:

import { useTranslation } from "react-i18next";

function ProductInfo() {
  // Specify the namespace to load
  const { t } = useTranslation("product");
  // NOTE: without passing in a namespace, the above hook would use `translation` namespace by default.
  // Since we don't have such namespace in our translations, the `t('namespace:key')` would still work,
  // but its autocomplete would no longer work in your IDE.

  return (
    <div>
      <h1>{t("title")}</h1>
      <p>{t("description")}</p>
      <button>{t("addToCart")}</button>
    </div>
  );
}

With multiple namespaces:

import { useTranslation } from "react-i18next";

function ProductPage() {
  // Load multiple namespaces at once
  const { t } = useTranslation(["home", "product"]);

  return (
    <div>
      <h1>{t("home:title")}</h1>
      <p>{t("product:description")}</p>
      <button>{t("product:addToCart")}</button>
    </div>
  );
}

With interpolation:

const { t } = useTranslation("cart");
const message = t("itemCount.other", { count: 5 }); // "Cart (5 items)"

With pluralization:

const { t } = useTranslation("cart");
const text = t("summary.itemsInCart", { count: 1 }); // "1 item in cart"
const text2 = t("summary.itemsInCart", { count: 3 }); // "3 items in cart"

In Non-Component Code

Use the getTranslation utility for tests, utilities, or any non-React code:

import { getTranslation } from "@salesforce/storefront-next-runtime/i18n";

// In tests
describe("ActionCard", () => {
  const { t } = getTranslation();

  test("shows edit button", () => {
    render(<ActionCard onEdit={vi.fn()} />);
    const button = screen.getByRole("button", { name: t("actionCard:edit") });
    expect(button).toBeInTheDocument();
  });
});

// In utility functions
export function getCountryName(countryCode: string): string {
  const { t } = getTranslation();
  return t(`countries:${countryCode}.name`, { defaultValue: countryCode });
}

// In form schemas (for Zod error messages)
const schema = z.object({
  email: z.string().email(t("error:validation.invalidEmail")),
});

In Route Loaders and Actions (Server-side)

Use getTranslation with the context parameter for server-side translations:

import { getTranslation, i18nextContext } from "@salesforce/storefront-next-runtime/i18n";
import type { LoaderFunctionArgs } from "react-router";

export function loader(args: LoaderFunctionArgs) {
  // Get translations by passing the context
  const { t } = getTranslation(args.context);
  const translatedTitle = t("product:title");

  // Get the current locale for formatting (if needed)
  const i18nextData = args.context.get(i18nextContext);
  const locale = i18nextData?.getLocale() ?? "en-GB";
  const date = new Date().toLocaleDateString(locale, {
    year: "numeric",
    month: "2-digit",
    day: "2-digit",
  });

  return { translatedTitle, date };
}

In actions with error handling:

import type { ActionFunctionArgs } from "react-router";
import { getTranslation } from "@salesforce/storefront-next-runtime/i18n";

export async function action(args: ActionFunctionArgs) {
  const { t } = getTranslation(args.context);

  try {
    // ... perform action
    return { success: true, message: t("product:addedToCart", { productName: "Widget" }) };
  } catch (error) {
    return { success: false, message: t("error:api.unexpectedError") };
  }
}

Adding New Translations

Approach: Single JSON File Per Language

All translations are stored in a single JSON file per language with namespace-based organization.

Understanding Namespaces

i18next uses the concept of namespaces to organize translations into logical groups. In our implementation, namespaces are simply the top-level keys in each translations.json file. For example, "common", "product", "checkout", and "myNewFeature" are all namespaces that help organize translations by feature or domain.

Core app namespaces use the camelCase naming convention, for example checkout or miniCart.

src/locales/en/translations.json:

{
  "common": {
    "loading": "Loading",
    "product": "the product"
  },
  "product": {
    "title": "Product Details",
    "addToCart": "Add to Cart",
    "greeting": "Hello, {{name}}!",
    "itemCount": {
      "zero": "No items",
      "one": "{{count}} item",
      "other": "{{count}} items"
    }
  },
  "myNewFeature": {
    "welcome": "Welcome to the new feature"
  }
}

src/locales/es/translations.json:

{
  "common": {
    "loading": "Cargando",
    "product": "el producto"
  },
  "product": {
    "title": "Detalles del Producto",
    "addToCart": "Agregar al Carrito",
    "greeting": "¡Hola, {{name}}!",
    "itemCount": {
      "zero": "Sin artículos",
      "one": "{{count}} artículo",
      "other": "{{count}} artículos"
    }
  },
  "myNewFeature": {
    "welcome": "Bienvenido a la nueva función"
  }
}

Using Your New Translations

// In React components
const { t } = useTranslation('myNewFeature');
<p>{t('welcome')}</p>

// In non-component code
const { t } = getTranslation();
const message = t('myNewFeature:welcome');

// Simple translation
<p>{t('title')}</p>

// With interpolation
<p>{t('greeting', { name: 'John' })}</p>

// With pluralization
<p>{t('itemCount', { count: items.length })}</p>

Extension Translations

Extensions can have their own translation files that are automatically discovered and integrated into the i18n system. This allows extension authors to keep translations co-located with their extension code.

File Structure for Extensions

Create translation files within your extension directory following this structure:

src/extensions/
├── my-extension/
│   ├── components/
│   ├── locales/
│   │   ├── en/
│   │   │   └── translations.json
│   │   └── es/
│   │       └── translations.json
│   └── index.ts

Namespace Convention

Extension translations automatically use the extPascalCase naming convention based on the extension folder name:

  • store-locator → extStoreLocator
  • bopis → extBopis
  • my-extension → extMyExtension

This convention prevents namespace collisions between extensions and core application translations.

How Locale Discovery Works

Important: The locale aggregation command (sfnext locales aggregate-extensions) is specifically for extension translations only. Main app translations in /src/locales/ are NOT aggregated by this command—they are imported directly.

The command scans two locations to discover all supported locales:

  1. Main app locales: /src/locales/{locale}/
  2. Extension locales: /src/extensions/{extension-name}/locales/{locale}/

The command merges locales from both sources and generates extension-only aggregation files under /src/extensions/locales/ for each discovered locale. This means:

  • If your main app supports Spanish (es-MX) but none of your extensions have Spanish translations, an empty aggregation file is still generated for es-MX
  • If an extension provides translations for a locale not in the main app, those translations are still aggregated (though the main app won't use them unless configured)
  • Extensions without a locales folder are automatically skipped - no error is thrown

Example scenario:

  • Main app: en-GB, es-MX, fr-FR translations
  • Extension A: en-GB, es-MX translations
  • Extension B: en-GB translations only
  • Extension C: No locales folder

Result: Extension aggregation files generated in /src/extensions/locales/ for en-GB, es-MX, and fr-FR:

  • en-GB/index.ts: Contains Extension A + Extension B translations only
  • es-MX/index.ts: Contains Extension A translations only
  • fr-FR/index.ts: Empty (no extensions have it)

Note: Main app translations remain in /src/locales/ and are not affected by this aggregation process.

Adding Translations to an Extension

1. Create the translation files:

Create locales/{lang}/translations.json within your extension directory for each supported language.

Example: src/extensions/bopis/locales/en/translations.json

{
  "deliveryOptions": {
    "title": "Delivery:",
    "pickupOrDelivery": {
      "shipToAddress": "Ship to Address",
      "pickUpInStore": "Pick Up in Store"
    }
  },
  "storePickup": {
    "title": "Store Pickup Location",
    "viewButton": "View",
    "closeButton": "Close"
  }
}

2. Translations are automatically aggregated:

When you run pnpm dev or pnpm build, the system automatically:

  • Discovers all extension translation files
  • Aggregates them with the appropriate namespace
  • Makes them available to your extension code

No manual configuration is required.

Using Extension Translations

In React Components:

import { useTranslation } from "react-i18next";

export function DeliveryOptions() {
  // Use your extension's namespace
  const { t } = useTranslation("extBopis");

  return (
    <div>
      <h3>{t("deliveryOptions.title")}</h3>
      <button>{t("deliveryOptions.pickupOrDelivery.pickUpInStore")}</button>
    </div>
  );
}

In Non-Component Code:

import { getTranslation } from "@salesforce/storefront-next-runtime/i18n";

export function getDeliveryMessage() {
  const { t } = getTranslation();
  // Use namespace prefix with colon
  return t("extBopis:deliveryOptions.title");
}

In Route Loaders/Actions:

import { getTranslation } from "@salesforce/storefront-next-runtime/i18n";
import type { LoaderFunctionArgs } from "react-router";

export function loader(args: LoaderFunctionArgs) {
  const { t } = getTranslation(args.context);
  return {
    message: t("extBopis:storePickup.title"),
  };
}

Using a Different i18n Library

The SDK's i18n support (@salesforce/storefront-next-runtime/i18n) is built on i18next. If you prefer a different library (for example, next-intl, formatjs, lingui), you can replace the i18n layer entirely:

  1. Skip the SDK's i18n subpath: Don't import from @salesforce/storefront-next-runtime/i18n or @salesforce/storefront-next-runtime/i18n/client.
  2. Locale resolution still works: The site-context system (createSiteContextMiddleware, locale detection from URL/cookie/header, SiteProvider) is i18n-library-agnostic and handles determining the active locale.
  3. Write your own middleware: Replace src/middlewares/i18next.server.ts with a middleware that initializes your chosen library, reading the resolved locale from requestToLocaleMap (exported from @salesforce/storefront-next-runtime/site-context).
  4. Write your own client init: Replace the initI18next() call in root.tsx with your library's initialization.
  5. Bridge to SiteProvider: Pass the current language string to SiteProvider's language prop (it accepts a plain string, no i18next dependency).
  6. Chunk splitting still works: The Vite i18nPlugin splits any files matching /src/locales/([^/]+)/ into per-language chunks, regardless of i18n library.

The SDK separates locale resolution (which locale is active) from translation (turning keys into strings). Only the translation layer is i18next-specific.

Best Practices

  1. Namespace by Route/Feature: Organize translations by feature area (e.g., product, checkout, account)
  2. Use the Right Tool:
    • React components: Use useTranslation() hook
    • Everything else: Use getTranslation() function
      • Non-component code (tests, utilities, schemas): getTranslation()
      • Server-side loaders/actions: getTranslation(context)
  3. Use TypeScript: The project includes type-safe translations based on the English locale
  4. Interpolation: Use {{variable}} syntax in translation strings (not {variable})
  5. Pluralization: Use nested objects with zero, one, other keys for count-based translations
  6. Lazy Loading: Client-side translations are loaded on-demand when first requested
  7. Fallback Chain: Missing translations fall back to the configured fallbackLng (English)

Type Safety

The project is configured for type-safe translations. TypeScript will autocomplete available keys and warn about missing translations:

// ✅ TypeScript knows these keys exist
const { t } = useTranslation("product");
t("title");
t("addToCart");

// With namespace prefix in non-component code
const { t } = getTranslation();
t("product:title");
t("cart:empty.title");

// ❌ TypeScript will warn about this
t("nonexistent.key");

Type definitions are generated from the English locale (resources['en-GB']) in src/middlewares/i18next.server.ts:

declare module "i18next" {
  interface CustomTypeOptions {
    resources: typeof resources["en-GB"]; // Use `en-GB` as source of truth for the types
  }
}