DSFR components contain hard coded strings.
Theses strings can be switched from a langage to another with a provider.
When lang="en"
When lang="fr"
Integration with i18n libraries
Next.js i18n App Router
Next.js i18n Page Router
Other i18n library
A type safe internationalisation library for SPAs and Next.js
import { useLang } from "i18n";
defaultColorScheme: "system",
Example setup in Next.js / In a SPA.
DISCLAMER: I'm the author of i18nifty.
While I can confidently recommend it for SPAs, I have to warn you that using i18nifty in Next.js will force you to opt out from Automatic Static Optimization and bundle all your translations in the JavaScript bundle. SSR, SSO will work fine though.
Routing: Internationalization
At the bottom you have setup examples
Assuming you have configured Next so that you have a lang prop provided to you in the main layout:
import { i18n } from '../../i18n-config'
export async function generateStaticParams() {
return => ({ lang: locale }))
export default function Root({
}: {
children: React.ReactNode
params: { lang: string }
}) {
const { lang } = params;
return (
{...getHtmlAttributes({ defaultColorScheme, lang })}
<DsfrProvider lang={lang}>
Assuming you have enabled internationalized routing:
import { useRouter } from "next/router";
defaultColorScheme: "system",
useLang: () => {
const router = useRouter();
return router.locale;
It's up you you to remplace in the following example to remplace "fr" by the desired locale using to tooling exposed by your i18n library.
defaultColorScheme: "system",
useLang: () => "fr"

Adding translations or overwriting defaut text

The components usualy come with one or two translations by default, typically english (en), spanish (es) and sometime german (de). Illustration with the <DarkModeSwitch /> component.
You can add translation for extra language on a component basis, like so:
import { addAlertTranslations } from "@codegouvfr/react-dsfr/Alert";
lang: "zh-CN",
messages: {
hide message: "隐藏消息"
The above code adds chinese (zh-CN) support for the Alert component. You can call addAlertTranslations() wherever, just be sure it's evaluated before the first use of the component, here <Alert />.
You can also use this approach for overwiting the default text. Example:
import { addDisplayTranslations } from "@codegouvfr/react-dsfr/Display";
lang: "fr",
messages: {
"dark theme": "Thème sombre 🤩",
It goes without saying this is not a recommended customization of the Display Modal

With Next App Router

When utilizing Next in App Router mode, it's crucial to accurately add or overwrite translations at the proper location.
For components that you use as server components, such as <Header />, <Footer />, or the <Display /> modal, you should make calls to addXxxTranslation within app/layout.tsx.
For components used as client components, and those explicitly marked as client components like <Alert /> or <Tabs />, addXxxTranslation should be conducted in app/StartDsfr.tsx.