rest api - Wordpress search post using unicode

I'm working with wordpress rest api I need to searching WP posts with unicode character example searching on my site:

/?s=ngoại+tình

The results is OK The I applied to my api : API URL :

+tình

Code:

$arrayPostFilter = array (
        "orderby" => "publish_date",
        "s" => $_GET['keyword'], 
        "posts_per_page" => 20,     
        'numberposts'=>-1,
        "paged" => $paged
    );

It's have no result, no posts found

Do I have to setting anything relate to Unicode for query filter?