
Yesterday, I posted about [implementing i18n routing in a nextjs project](/garden/12-i18n-nextjs), focusing on the `app` folder and middleware setup. This post follows from that post with an `I18NLink` component that leverages our i18n set up to automatically prefix your links with the user's current language. This way, you can do something like this:

``` typescript
<I18NLink href="/settings">{t('settings', 'Settings')}</I18NLink>
```

And the link will automatically pick up the `lang` param to route to either `/settings` or (for example) `/es/settings` depending on the `lang` in the url.

Note: the `t` function is a stand in for a generic translation function that would take a key like `settings` and return a string or fallback to the second argument, which is "Settings".

## wrapping the `Link` component

The first thing we need to do is wrap NextJS's default `Link` component:

``` typescript
import type { ComponentProps } from 'react';
import React from 'react';
import Link from 'next/link';

export type I18NLinkType = Omit<ComponentProps<typeof Link>, 'as'> & {
  href: string;
};

function I18NLink({ children, href, ...props }: I18NLinkType) {
  return (
    <Link href={href} {...props}>
      {children}
    </Link>
  )
}
```

A few things are happening here:

1. We are creating a new `I18NLinkType` by taking the `Link` type and omitting `as` so we can use the component polymorphically.
2. We are defining `href` as a string since `Link` potentially accepts a `URL`.
3. We then create a function that's more or less a pass-through: take the `href` and `children` and just pass them to `Link`.

This isn't doing too much yet. We need to hook it into the `useParams` hook.

## get current `lang` param

Let's update the component:

``` typescript
import { useParams } from 'next/navigation';

// generic import of your default language
import { defaultLanguage } from 'settings';

function I18NLink({ children, href, ...props }: I18NLinkType) {
  const params = useParams();
  const currentLanguage = (params?.lang as string) || defaultLanguage;

  return (
    <Link href={`${currentLanguage}${href}`} {...props}>
      {children}
    </Link>
  )
}
```

Note that `params` could be `null` or an empty `Record`, so we want to coerce `lang` as a string.

This isn't a bad solution, but we're going to run into a few problems:

1. We don't want to prepend the `defaultLanguage` if we don't have to since it'll cause an extra redirect in the middleware.
2. We can't use the Link generically since it'll only work for relative paths. If we pass an absolute or external route, the url will be malformed.

## checking incoming href

What we need to do to prevent the above is check the incoming `href` and make decisions about what `href` to actually pass to `Link`.

``` typescript
function getPath(path?: string | null) {
  // 1.
  if (!path) {
    return ['en', ''];
  }

  // 2.
  const pathArray = path.split('/').filter((x) => !!x);

  // 3. empty array
  if (pathArray.length === 0) {
    return ['en', ''];
  }

  // 4.
  const [lang, ...restPath] = pathArray;

  // 5.
  if (languageArray.includes(lang)) {
    return [lang, restPath.join('/')];
  }

  // 6.
  return ['en', pathArray.join('/')];
}


function getPrefixedUrl(href: string, currentLanguage: string) {
  // 1. handle absolute links
  if (/^((http|https):\/\/)/.test(href)) {
    return href;
  }

  // 2.
  const [, tail] = getPath(href);

  // 3.
  if (currentLanguage === defaultLanguage) {
    return `/${tail}`;
  }

  // 4.
  return `/${currentLanguage}/${tail}`;
}
```

Let's start with `getPrefixedUrl`:

1. If the `href` starts with `http` or `https`, we should follow the absolute route provided.
2. Otherwise, we want to get the url path without the `lang` param if it's provided.
3. If the `currentLanguage` is also the default language, just pass the `tail` of the path
4. Otherwise, prepend the current language to the `tail` of the path

`getPath` might seem a little extraneous or verbose, but it's meant to help avoid issues with passing around the root and with overriding the `lang` provided in the url.

1. If the `path` is null, return an array we can use to route the user to the root of the site.
2. Take the path, and split it at `/`. The array is going to be easier to work with.
3. If the array is empty because `path === '/'`, return an array we can use to route the user to the root of the site. 
4. We want to deal with just `restPath` if (and only if) the first part of the url is actually an `lang` param.
5. We do a check to ensure that `lang` is include in our `langaugeArray`, which tells us we can safely use `restPath`
6. Otherwise we want to return the whole path we were provided

With these helper functions, we can update the component:

``` typescript
function I18NLink({ children, href, ...props }: I18NLinkType) {
  const params = useParams();
  const currentLanguage = (params?.lang as string) || defaultLanguage;
  const prefixedHref = getPrefixedUrl(href, currentLanguage);
  return (
    <Link href={prefixedHref} {...props}>
      {children}
    </Link>
  )
}
```

### bonus: anchor or `Link`

If you want to escape the client cache with a "hard" route, you might want to be able to use *either* an anchor or `Link` component:

``` typescript
export type I18NLinkType = Omit<ComponentProps<typeof Link>, 'as'> & {
  isAnchor?: boolean;
  href: string;
};

function I18NLink({ children, href, isAnchor, ...props }: I18NLinkType) {
  const params = useParams();
  const currentLanguage = (params?.lang as string) || defaultLanguage;
  const prefixedHref = getPrefixedUrl(href, currentLanguage);
  if (isAnchor) {
    return (
      <a href={prefixedHref} {...props}>
        {children}
      </a>
    );
  }

  return (
    <Link href={prefixedHref} {...props}>
      {children}
    </Link>
  )
}
```

We can just use a `boolean` and render an anchor tag based on `isAnchor` if passed.

## wrapping up

It would be great to have a more built in way to handle internationalization in NextJS, however it only requires a little bit of boilerplate to get a full fledged i18n setup, including automatic i18n routing with NextJS's default `Link` component.

Check out the full gist [here](https://gist.github.com/inadeqtfuturs/5281c16d825208fb36fec0ecb79d4d65).


i18n routing with nextjs 13 app router

automatic i18n linking with nextjs 13 app router


Recently at [graveflex](https://graveflex.com), I created a learning platform for one of our clients. In addition to mutli-tenant authentication and authorization, the whole platform needed to be translatable. Having done a handful of i18n sites in the past using [NextJS's pages router](https://nextjs.org/docs/pages/building-your-application/routing/internationalization), I was surprised to find how minimal the [app router] documentation was, largely leaving the complexity of routing to external packages.

Initially, I assumed that I could use one of these external packages to handle routing, but I ran into a few problems with each:

- [next-intl](https://next-intl-docs.vercel.app/docs/getting-started/app-router-server-components): needed more control inside middleware and didn't want to opt into what seemed like a fairly complex boilerplate set up they provide for `Auth.js`.
- [next-international](https://next-international.vercel.app/docs/app-setup): similar to `next-intl`, but we also didn't have the need to manage transations in the same way given our data structure and CMS.
- [next-i18n-router](https://github.com/i18nexus/next-i18n-router/): same concern about middleware, though, of all the solutions NextJS links out to, this one seems the like the most streamlined.

It seemed like it might just be easiest and that we could maintain the most control if we rolled out our own middleware. What we wanted was to define a set of potential locales (English and Spanish), and define one as the default locale. When the user was routing using the default locale, we didn't want the locale param to be displayed to the end user, however, the locale params *should* display when routing in any locale that is not the default.

``` javascript
`/` -> home
`/es` -> home translated
`/some-route` -> settings
`/es/settings` -> settings translated
```

The process of setting up the routing required two things: first, we need to wrap all routes inside the `app` folder in `[lang]` (or any dynamic route), and then set up the middleware to handle rewrites and redirects. The middleware needed to do the following:

1. check if there is a locale in the path
2. if there's no locale, we assume it's the default locale. however, *rewrite* the path to include the default locale so we have access to it from `useParams()`
3. if the locale is the default locale, redirect without the locale so the user doesn't see it in the url
4. if the locale is not valid, redirect the path with the default locale
5. otherwise, the locale is valid and the request should just pass through the middleware

While the above is opinionated, it defines, in general, how all of packages listed above work. Additionally, writing the middleware alerted us to handful of problems we might have run into otherwise.

## `app` set up

Following the conventions of i18n packages and NextJS's docs, we started by wrapping the entire file structure in the `app` folder in `[lang]`.

``` javascript
└── app/[lang]/
    ├── (public)
    │   ├── layout.tsx
    │   └── login/
    │       ├── LoginPage.tsx
    │       └── page.tsx
    └── (user)
        ├── layout.tsx
        ├── not-found.tsx
        ├── page.tsx
        ├── [...not-found]/
        │   └── page.tsx
        └── settings/
            ├── page.tsx
            └── layout.tsx
```

> Note: this is an overly simplified file structure to explain how the routing works.

There are a handful of things that happen when you set the routing up this way:

1. Because every route is nested under `[lang]`, you will always have access to the `lang` param either as a parameter in server components like `layout` or `page`, as well as `useParams`.
2. Defining [route groups](https://nextjs.org/docs/app/building-your-application/routing/route-groups) as `(public)` and `(user)` allows us to separate the layouts, pages, and general data fetching we're doing for either authenticated or unauthenticated users.
3. Note the [catch-all segment](https://nextjs.org/docs/app/building-your-application/routing/dynamic-routes#catch-all-segments) in the `(user)` folder -- this is a file that just returns `notFound()` so that we can (1) translate the not found page and (2) correctly display that page within the authenticated navigation shell.

## middleware set up

Knowing how we want the middleware to behave, we can break the function down into a few steps:

### set language config

First, we set up some constants to reference throughout the middleware.

``` javascript
const languages = ['en', 'es'];
const defaultLanguage = 'en'
```

### check for locale in path

``` javascript
import type { NextRequest } from 'next/server'

export async function middleware(request: NextRequest) {
  const { pathname } = request.nextUrl;
  const matches = pathname.match('^/([a-z]{2})(/.*)?$');
  const language = !matches ? 'en' : matches[1];
}
```

Inside the actual middleware function, we grab the `pathname` from the request and run it against a regex pattern that's looking for `/xx/` as the first part of the pathname. If you needed language and locale support, you could rewrite the regex to suit those needs. Otherwise, we set `langauge` to be either the default language, or the language passed in the path.

### handle no locale

``` javascript
export async function middleware(request: NextRequest) {
  // ...previous code

  // no locale -- assume en and rewrite so nextjs gets lang params
  // but user sees url without language
  if (!matches) {
    // note `newURL` 
    return NextResponse.rewrite(newURL(`/${defaultLanguage}${pathname}`, request));
  }
}
```

When there is no locale, we *rewrite* the request so that NextJS sees locale included in the URL, while the user does NOT see the locale in the URL.

Note the `newURL` function: we can't just pass the pathname because we're lose other parts of the url path. We knew we wanted to maintain (at the least) the query string params, so we wrote a function to pass those along:

``` javascript
// construct new url based on desired path and original request
function newURL(url: string, originalRequest: NextRequest) {
  const originalUrl = originalRequest.url;
  const query = originalRequest.nextUrl.searchParams.toString();

  const nextUrl = query ? `${url}?${query}` : url;

  return new URL(nextUrl, originalUrl);
}
```

### redirect if default locale is included

``` javascript
export async function middleware(request: NextRequest) {
  // ...previous code
  // redirect if defaultLanguage === language
  if (language === defaultLanguage) {
    return NextResponse.redirect(
      newURL(
        pathname.replace(`/${defaultLanguage}`, '/').replace('//', '/'),
        request
      )
    );
  }
}
```

If the `language` matches the `defaultLanguage`, we want to remove the language from the url so it can be handled by the rewrite.

### handle invalid language

``` javascript
export async function middleware(request: NextRequest) {
  // ...previous code
  const invalidLanguage = !languages.includes(languageFromPath);
  if (invalidLanguage) {
    return NextResponse.redirect(newURL(`/${defaultLanguage}${currPath}`, request));
  }

}
```

If the language we got from the path is not invluded in our languages array, route to the path but relative to the default language to either `200` throw a `404`.


### allow passthrough

If we have a valid language, we can just pass the request through.

``` javascript
export async function middleware(request: NextRequest) {
  // ...previous code
  return NextResponse.next();
}
```

### clean up

One thing you might notice is that we're not taking advantage of headers to pass the language around in requests. The main reason for this is simplicity and visibility: we don't want to obfuscate the user preferred language in a header when we can just have it as part of the URL.

However, we could (and should) leverage the browser's built-in language handling. To do this, we can wrap our responses in a helper function:

``` javascript
function addLanguageRespHeader(resp: NextResponse, lang: string = 'en') {
  resp.headers.set('Content-Language', lang);

  return resp;
}
```

Just pass along the `lang` as the second argument to set the header value:

``` javascript
  // ex.
  return addLanguageRespHeader(NextResponse.next(), languageFromPath);
```

## wrapping up

It might seem like a lot, but we can break the functionality of our middleware down to a few explicit steps and write the code ourselves. In the future, we'll probably package this along with instructions for composing it with other middleware.
