# Building a Language Switcher for Next.js

> In this article, we create a Language dropdown to switch to another language using Next.js and next-i18n.

*Published: 2022-10-12*
*Canonical: https://makerkit.dev/blog/tutorials/language-switcher-nextjs*

---

[next-i18n-next](https://github.com/i18next/next-i18next) is a popular Next.js library for managing translations and i18n in your application or website.

In this article, I want to show you how I made a dynamic language switcher for the Makerkit Next.js template and how you can copy and reuse it in your own applications.

My goal was to automatically load, display and translate the available languages based on the Next.js i18n configuration: this is finally possible thanks to the fantastic `Intl` Browser API.

For example, let's assume the below is your Next.js i18n configuration:

 ```js {% title="next-i18next.config.js" %}
const config = {
  i18n: {
    defaultLocale: 'en',
    locales: ['en', 'it'],
  },
  fallbackLng: {
    default: ['en'],
  },
  localePath: resolve('./public/locales'),
};
```

The component **automatically renders** a dropdown with two languages: `Italian` and `English`. Furthermore, the language names **will be translated into the currently selected language**.

### Building a Language Selector for Next.js

Let's name our component `LanguageSwitcher`. This component will also emit a callback with the selected language to its parent, which can be helpful if you want to persist the choice somewhere.

```tsx
const LanguageSwitcher: React.FC<{
  onChange?: (locale: string) => unknown;
}> = ({ onChange }) => {}

export default LanguageSwitcher;
```

Let's define some of the constants we're going to use:

```tsx
const { i18n } = useTranslation();
const { language: currentLanguage } = i18n;
const router = useRouter();
const locales = router.locales ?? [currentLanguage];
```

Thanks to `router.locales`, we can retrieve the languages added to the Next.js configuration. This helps us make the component configuration-less.

Next, we're going to instantiate an `Intl.DisplayNames` instance: this powerful API will return the language name in the selected language:

```tsx
 const languageNames = useMemo(() => {
  return new Intl.DisplayNames([currentLanguage], {
    type: 'language',
  });
}, [currentLanguage]);
```

We can use the `Intl.DisplayNames` API in the following way:

```tsx
console.log(
  languageNames.of(lang)
)
```

For example, if `currentLanguage` is `English` and `lang` is `it` (Italian), the above will display `Inglese`, English in Italian.

Let's now define what happens when a language is switched:

1. Using `router.push`, we can pass the selected `locale`. This will cause Next.js to re-render the page with the new locale's translations
2. We emit the `onChange` callback if it's passed from the parent component
3. We set the local state with `setValue`

```tsx
const [value, setValue] = useState({
  value: i18n.language,
  label: capitalize(languageNames.of(currentLanguage) ?? currentLanguage),
});

const switchToLocale = useCallback(
  (locale: string) => {
    const path = router.asPath;

    return router.push(path, path, { locale });
  },
  [router]
);

const languageChanged = useCallback(
  async (option: ListBoxOptionModel<string>) => {
    setValue(option);

    const locale = option.value;

    if (onChange) {
      onChange(locale);
    }

    await switchToLocale(locale);
  },
  [switchToLocale, onChange]
);
```

And now it's time to render our component with a selector element: you can use your own, the native HTML `select`, or Makerkit's `ListBox`:

```tsx
return (
  <ListBox value={value} setValue={languageChanged}>
    {locales.map((locale) => {
      const label = capitalize(languageNames.of(locale) ?? locale);

      const option = {
        value: locale,
        label,
      };

      return <ListBoxOption key={locale} option={option} />;
    })}
  </ListBox>
);
```

Of course, you should adapt the above to the HTML component you have access to.

Below, you can find a demo:

{% Video src="/assets/images/posts/language-selector.mp4" /%}

### Full Source Code

Below is the full source code of the component:

```tsx
import { useRouter } from 'next/router';
import { useCallback, useMemo, useState } from 'react';
import { useTranslation } from 'next-i18next';

import ListBox, { ListBoxOptionModel } from '~/core/ui/ListBox/ListBox';
import ListBoxOption from '~/core/ui/ListBox/ListBoxOption';

const LanguageSwitcher: React.FC<{
  onChange?: (locale: string) => unknown;
}> = ({ onChange }) => {
  const { i18n } = useTranslation();
  const { language: currentLanguage } = i18n;
  const router = useRouter();
  const locales = router.locales ?? [currentLanguage];

  const languageNames = useMemo(() => {
    return new Intl.DisplayNames([currentLanguage], {
      type: 'language',
    });
  }, [currentLanguage]);

  const [value, setValue] = useState({
    value: i18n.language,
    label: capitalize(languageNames.of(currentLanguage) ?? currentLanguage),
  });

  const switchToLocale = useCallback(
    (locale: string) => {
      const path = router.asPath;

      return router.push(path, path, { locale });
    },
    [router]
  );

  const languageChanged = useCallback(
    async (option: ListBoxOptionModel<string>) => {
      setValue(option);

      const locale = option.value;

      if (onChange) {
        onChange(locale);
      }

      await switchToLocale(locale);
    },
    [switchToLocale, onChange]
  );

  return (
    <ListBox value={value} setValue={languageChanged}>
      {locales.map((locale) => {
        const label = capitalize(languageNames.of(locale) ?? locale);
        const option = {
          value: locale,
          label,
        };

        return <ListBoxOption key={locale} option={option} />;
      })}
    </ListBox>
  );
};

function capitalize(lang: string) {
  return lang.slice(0, 1).toUpperCase() + lang.slice(1);
}

export default LanguageSwitcher;
```