Arabic Letters

The Arabic script has been adopted for use in a wide variety of languages besides Arabic, including Persian, Malay and Urdu which are not Semitic. Such adaptations may feature altered or new characters to represent phonemes that do not appear in Arabic phonology. For example, the Arabic language lacks a voiceless bilabial plosive (the [p] sound), so many languages add their own letter to represent [p] in the script, though the specific letter used varies from language to language. These modifications tend to fall into groups: all the Indian and Turkic languages written in the Arabic script tend to use the Persian modified letters, whereas the languages of Indonesia tend to imitate those of Jawi. The modified version of the Arabic script originally devised for use with Persian is known as the Perso-Arabic script by scholars.

In the cases of Bosnian, Kurdish, Kashmiri, and Uyghur writing systems, vowels are mandatory. The Arabic script can therefore be used in both abugida and abjad, although it is often strongly, erroneously connected to the latter.

Use of the Arabic script in West African languages, especially in the Sahel, developed with the spread of Islam. To a certain degree the style and usage tends to follow those of the Maghreb (for instance the position of the dots in the letters fāʼ and qāf). Additional diacritics have come into use to facilitate writing of sounds not represented in the Arabic language. The term ʻAjamī, which comes from the Arabic root for "foreign," has been applied to Arabic-based orthographies of African languages.

Source: wikipedia