Add internationalization support with astro-i18next integration

- Implemented astro-i18next for multi-language support, including English, Dutch, and Italian.
- Configured default locale and language fallback settings.
- Defined routes for localized content in the configuration.
- Updated package.json and package-lock.json to include new dependencies for i18next and related plugins.

node_modules/i18next-fs-backend/lib/extname.js

@@ -0,0 +1,4 @@
+export default (filename) => {
+  if (filename.indexOf('.') < 0) return undefined
+  return `.${filename.split('.').pop()}`
+}