The Arabic script has been adapted 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 sound), therefore many languages add their own letter to represent in the script, though the specific letter used varies from language to language. These modifications tend to fall into groups: 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.