Use str_plit() instead of mb_str_split().

src/Base.php

@@ -43,7 +43,7 @@ public function __construct($data = [])
                 break;
             case \is_string($data):
                 $this->source = static function () use ($data) {
-                    foreach (mb_str_split($data) as $key => $value) {
+                    foreach (\str_split($data) as $key => $value) {
                         yield $key => $value;
                     }
                 };