Pre-render locale-specific variants

There are still some places that dynamically determine the user's locale
based on request headers (e.g. /api/v1/user/email), but most pages
should now be prerendered in a specific locale, and the user should be
redirected to those pages when they don't specify the locale in the URL.
This also means that users can now be linked to specific locales.

Theoretically, this should help both with (localised) search ranking, as
well as with performance (which also influences at least Google's
ranking).

A good addition would be a language switcher, so that users who get
linked to a locale that's not theirs, can still switch.

Author: Vinnl

functional-tests/tests/global-teardown.ts

@@ -47,7 +47,7 @@ async function deleteTestUserAccounts(browser: Browser) {
       name: "Delete account",
     });
     await deleteButtonConfirm.click();
-    await page.waitForURL(`${getBaseTestEnvUrl()}/`);
+    await page.waitForURL(`${getBaseTestEnvUrl()}/en`);
 
     await page.goto(manageFxaAccountUrl!);
     await page.getByRole("link", { name: "Delete Account" }).click();

jest.config.cjs

@@ -121,6 +121,9 @@ const customJestConfig = {
     "react-dom/server": "react-dom/server.edge",
     // Force module uuid to resolve with the CJS entry point, because Jest does not support package.json.exports. See https://github.com/uuidjs/uuid/issues/451
     uuid: require.resolve("uuid"),
+    // For some reason Jest isn't able to load `.storybook/preview` from `jest.setup.ts`
+    // when running `npm test`, but this line fixes it:
+    "^.*\\.storybook/preview$": "<rootDir>/.storybook/preview.tsx",
   },
 
   // An array of regexp pattern strings, matched against all module paths before considered 'visible' to the module loader

package.json

@@ -17,7 +17,7 @@
     "build": "npm run build-glean && npm run build-nimbus && next build && npm run build-cronjobs",
     "cloudrun": "npm run db:migrate && npm start",
     "start": "next start",
-    "lint": "stylelint '**/*.scss' && prettier --check './src' && eslint --max-warnings=0 . && tsc -p tsconfig.json --noEmit && npm run validate-nimbus",
+    "lint": "stylelint '**/*.scss' && prettier --check './src' && eslint --max-warnings=0 . && next typegen && tsc -p tsconfig.json --noEmit && npm run validate-nimbus",
     "fix": "prettier --write './src' && eslint --fix . && stylelint --fix '**/*.scss'",
     "test": "npm run build-nimbus && jest \"\\.(spec|test)\\.ts\"",
     "test-integrations": "npm run build-nimbus && jest \"\\.integration\\.ts\" --coverage=false --runInBand",