You can use this WordPress virtual Arabic keyboard plugin to type using in Arabic language without any 3rd party Software or Sites.Currently this plugin only displaying in site home page content.
After activating this plugin, the keyboard is automatically adding to the home page content.
You can use [wp-arabic-virtual-keyboard] shortcode to display the keyboard any page or post.
About the Arabic alphabet:
The Arabic alphabet has 28 letters. Adaptations of the Arabic script for other languages, such as Persian, Ottoman, Sindhi, Urdu, Malay or Pashto, Arabi Malayalam, have additional letters, shown below. There are no distinct upper and lower case letter forms.
Many letters look similar but are distinguished from one another by dots (’i‘j?m) above or below their central part, called rasm. These dots are an integral part of a letter, since they distinguish between letters that represent different sounds. For example, the Arabic letters transliterated as b and t have the same basic shape, but b has one dot below, ?, and t has two dots above, ?.
Both printed and written Arabic are cursive, with most of the letters within a word directly connected to the adjacent letters.