feat: add i18n support for 14 languages

Add translations for de, es, es-419, fr, hi, id, it, nl, pl, pt, pt-BR, sr, sv, zh-Hans-CN
to match upstream Indiekit's supported locales. Also add missing localesDirectory getter.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

index.js

@@ -1,4 +1,5 @@
 import path from "node:path";
+import { fileURLToPath } from "node:url";
 
 import express from "express";
 
@@ -29,6 +30,14 @@ export default class MicrosubEndpoint {
     this.mountPath = this.options.mountPath;
   }
 
+  /**
+   * Locales directory path
+   * @returns {string} Path to locales directory
+   */
+  get localesDirectory() {
+    return path.join(path.dirname(fileURLToPath(import.meta.url)), "locales");
+  }
+
   /**
    * Navigation items for Indiekit admin
    * @returns {object} Navigation item configuration