feat: Browser language detection

Adds ability to automatically redirect new users to their favorite language based on browser's
accept-language

Closes nuxt-modules#37

lib/module.js

@@ -10,7 +10,9 @@ module.exports = function (moduleOptions) {
     loadLanguagesAsync: false,
     langDir: 'lang/',
     langFiles: {},
-    ignorePaths: []
+    ignorePaths: [],
+    detectBrowserLanguage: false,
+    redirectCookieKey: 'redirected'
   }
   const options = merge(defaults, moduleOptions, this.options.i18n)
 

lib/templates/i18n.routing.middleware.js

@@ -1,6 +1,7 @@
+import cookie from 'cookie';
 import middleware from './middleware'
 
-middleware['i18n'] = function ({ app, route, redirect, error, hotReload }) {
+middleware['i18n'] = function ({ app, req, res, route, params, redirect, error, hotReload }) {
   const locales = <%= JSON.stringify(options.locales) %>
   const localeCodes = locales.map(l => l.code)
   const defaultLocale = '<%= options.defaultLocale %>'
@@ -14,6 +15,32 @@ middleware['i18n'] = function ({ app, route, redirect, error, hotReload }) {
     localeCodes.includes('<%= options.redirectRootToLocale %>')) {
     redirect('/<%= options.redirectRootToLocale %>/')
   }
+
+  // Handle browser language detection
+  if (<%= options.detectBrowserLanguage %> && req && route.name) {
+    const cookieKey = '<%= options.redirectCookieKey %>';
+    const cookies = cookie.parse(req.headers.cookie);
+    // Redirect only if cookie not set yet
+    if (!cookies[cookieKey]) {
+      const browserLocale = req.headers['accept-language'].split(',')[0].toLocaleLowerCase().substring(0, 2)
+      // Set cookie
+      if (res) {
+        const date = new Date();
+        const redirectCookie = cookie.serialize(cookieKey, 1, {
+          expires: new Date(date.setDate(date.getDate() + 365))
+        })
+        res.setHeader('Set-Cookie', redirectCookie);
+      }
+      // Redirect
+      if (browserLocale !== app.i18n.locale && localeCodes.indexOf(browserLocale) !== -1) {
+        app.i18n.locale = browserLocale
+        redirect(app.localePath(Object.assign({}, route , {
+          name: app.getRouteBaseName()
+        })));
+      }
+    }
+  }
+
   // Get locale from params
   let locale = defaultLocale
   locales.forEach(l => {

package.json

@@ -34,6 +34,7 @@
     ]
   },
   "dependencies": {
+    "cookie": "^0.3.1",
     "vue-i18n": "^7.3.2",
     "vue-i18n-extensions": "^0.1.0"
   },