feat(i18n): translation files DE/EN/UK/RU + layout integration (closes #74)

app/Controllers/Controller.php

@@ -4,8 +4,14 @@ declare(strict_types=1);
 
 namespace App\Controllers;
 
+use App\Core\I18n;
+use App\Core\Locale;
 use App\Core\View;
 
+/**
+ * Base controller — injects i18n globals (locale, t() helper, locale switcher)
+ * into every render() call so views can use `$t('key')` and `$locale` directly.
+ */
 abstract class Controller
 {
     protected View $view;
@@ -15,9 +21,28 @@ abstract class Controller
         $this->view = new View();
     }
 
+    /**
+     * Render a view inside a layout.
+     *
+     * @param array<string,mixed> $data
+     */
     protected function render(string $view, array $data = [], string $layout = 'main'): void
     {
-        foreach ($data as $key => $value) {
+        $locale = LocaleController::current();
+        $i18n   = static fn (string $key, array $params = []): string => I18n::t($key, $params, $locale);
+
+        $globals = [
+            'locale'          => $locale,
+            't'               => $i18n,
+            'locale_switcher' => static function (string $currentPath) use ($locale): string {
+                $switcher = new LocaleSwitcher($locale, $currentPath);
+                return $switcher->render();
+            },
+        ];
+
+        $merged = array_merge($globals, $data);
+
+        foreach ($merged as $key => $value) {
             $this->view->assign($key, $value);
         }
         $this->view->render($view, $layout);