Fix compatibility with the latest version of Lingui

* Update to resolve incompatiblity with breaking changes in Lingui
* Somewhat hacky approach in _document.js to resolve the issue (changed export type to cjs, use string replace)
* Now also checks hostname for the locale (e.g. `en.example.com`, `fr.example.com`)

.linguirc

@@ -1,5 +1,5 @@
 {
-  "compileNamespace": "window.LINGUI_CATALOG",
+  "compileNamespace": "cjs",
   "fallbackLocale": "en",
   "sourceLocale": "en",
   "localeDir": "<rootDir>/locale",

pages/_document.js

@@ -1,19 +1,21 @@
 import NextDocument, { Head, Main, NextScript } from "next/document";
 
-const supportedLocale = ["en", "fr", "es"];
+const supportedLocales = ["en", "fr", "es"];
 
 export default class Document extends NextDocument {
   static async getInitialProps(ctx) {
-    const queryLocale = ctx.query.locale;
-    const locale = supportedLocale.find(l => l === queryLocale)
-      ? queryLocale
-      : "en";
-
-    const linguiCatalog = await import(`raw-loader!../locale/${locale}/messages.js`).then(
-      mod => mod.default
-    );
-
     const initialProps = await NextDocument.getInitialProps(ctx);
+
+    // Try to detect locale from:
+    // * locale query string param (e.g. ?locale=fr)
+    // * hostname (e.g. `en.example.com`, `fr.example.com`, etc)
+    // First locale specified in supportedLocales is the default fallback used
+    const detectedLocale = ctx.query.locale || ctx.req.headers.host.split('.')[0];
+    const locale = supportedLocales.find(l => l === detectedLocale) ? detectedLocale : supportedLocales[0];
+
+    // Load source for current translation file and inject into page (hacky!)
+    let linguiCatalog = await import(`raw-loader!../locale/${locale}/messages.js`).then(mod => mod.default);
+    linguiCatalog = linguiCatalog.replace('module.exports = {', 'window.LINGUI_CATALOG = {');
 
     return { ...initialProps, linguiCatalog };
   }