In addition to previous notes, the direction of the text depends on the HTML dir
attribute, an example of multilanguage page:
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>sample arabic language</title>
</head>
<body>
<p lang="ar" dir="rtl">مرحبا</p>
<p>hello</p>
</body>
</html>
If your page is not mixed and you have only Arabic, then change it to:
<!DOCTYPE html>
<html lang="ar" dir="rtl">
<head>
<meta charset="utf-8">
<title>sample arabic language</title>
</head>
<body>
<p>مرحبا</p>
</body>
</html>
The rtl
value stands for right-to-left. I don't know Wordpress, plus I don't know if you're using an uri segment to define the language in use, but it should be easy to set lang and dir attributes on the fly.