fix(testing): Fix fake provider reverting strings with emojis

Signed-off-by: Joas Schilling <coding@schilljs.com>

Author: nickvergessen

apps/testing/lib/Provider/FakeTranslationProvider.php

@@ -25,6 +25,14 @@ public function getAvailableLanguages(): array {
 	}
 
 	public function translate(?string $fromLanguage, string $toLanguage, string $text): string {
-		return strrev($text);
+		return $this->mb_strrev($text);
+	}
+
+	protected function mb_strrev(string $str): string {
+		$r = '';
+		for ($i = mb_strlen($str); $i >= 0; $i--) {
+			$r .= mb_substr($str, $i, 1);
+		}
+		return $r;
 	}
 }