diff --git a/apps/testing/lib/Provider/FakeTextProcessingProvider.php b/apps/testing/lib/Provider/FakeTextProcessingProvider.php
index 7a318196ab3d2..ffa7d16ef242e 100644
--- a/apps/testing/lib/Provider/FakeTextProcessingProvider.php
+++ b/apps/testing/lib/Provider/FakeTextProcessingProvider.php
@@ -18,10 +18,21 @@ public function getName(): string {
 	}
 
 	public function process(string $prompt): string {
-		return strrev($prompt) . ' (done with FakeTextProcessingProvider)';
+		return $this->mb_strrev($prompt) . ' (done with FakeTextProcessingProvider)';
 	}
 
 	public function getTaskType(): string {
 		return FreePromptTaskType::class;
 	}
+
+	/**
+	 * Reverse a miltibyte string.
+	 *
+	 * @param string $string The string to be reversed.
+	 * @return string The reversed string
+	 */
+	private function mb_strrev(string $string): string {
+		$chars = mb_str_split($string, 1);
+		return implode('', array_reverse($chars));
+	}
 }
diff --git a/apps/testing/lib/Provider/FakeTextProcessingProviderSync.php b/apps/testing/lib/Provider/FakeTextProcessingProviderSync.php
index f6fe63c0f8275..55c0cfef3bfe7 100644
--- a/apps/testing/lib/Provider/FakeTextProcessingProviderSync.php
+++ b/apps/testing/lib/Provider/FakeTextProcessingProviderSync.php
@@ -20,7 +20,7 @@ public function getName(): string {
 	}
 
 	public function process(string $prompt): string {
-		return strrev($prompt) . ' (done with FakeTextProcessingProviderSync)';
+		return $this->mb_strrev($prompt) . ' (done with FakeTextProcessingProviderSync)';
 	}
 
 	public function getTaskType(): string {
@@ -30,4 +30,15 @@ public function getTaskType(): string {
 	public function getExpectedRuntime(): int {
 		return 1;
 	}
+
+	/**
+	 * Reverse a miltibyte string.
+	 *
+	 * @param string $string The string to be reversed.
+	 * @return string The reversed string
+	 */
+	private function mb_strrev(string $string): string {
+		$chars = mb_str_split($string, 1);
+		return implode('', array_reverse($chars));
+	}
 }