🌐 Add Polish translations and expand Spanish dictionaries

- Added a new `lang/pl.json` file with comprehensive Polish translations.
- Enhanced `lang/es.json` with additional Spanish keys and phrases for better coverage.

lang/pl/pagination.php

@@ -0,0 +1,8 @@
+<?php
+
+declare(strict_types=1);
+
+return [
+    'next'     => 'Następna &raquo;',
+    'previous' => '&laquo; Poprzednia',
+];