Lao or Laotian (ພາສາລາວ, phasa lao, pronounced [‘phaːsaː ‘láːo]) is a tonal language of the Tai–Kadai language family. It is the official language of Laos, and also spoken in the northeast of Thailand, where it is usually referred to as Isan language. The Lao script was slowly standardised in the Mekong River valley after the various Tai principalities of the region were merged under the rule of the Kingdom of Lan Xang in the 14th century. It is an abugida script (where only the consonants have signs and the vowels are “implied”), traditionally written from left to right Writing system: Lao in Laos, Thai in Thailand Official language in: Laos