Article by Pham Thi Vanh Anh, ASEAN Weblog Correspondent from Vietnam
The reason why I choose handwriting and language as an element to compare the difference and similarity of Indochina is that handwriting and language are important factors that affect to the culture of each country, especially the presence of French has a profound influence to the development of handwriting and language in Cambodia and Vietnam.
Vietnamese, formerly known under French colonization as Annam, is the national and official language of Vietnam. It is the mother tongue of the Vietnamese people.
Vietnamese script has the origin from Chinese and clearly we can learn that Vietnamese script spent three periods. The first is Han Viet (Sino-Vietnamese). The second is Nom appeared in the 18th century. The third is Quoc Ngu (Current national language). Vietnam is lucky to have European priests who changed Asian handwriting into Latin handwriting. Vietnam is affected by two civilizations, Asian and Western; therefore Vietnamese language is very popular. The first period is dominated by French. When France invaded Vietnam in the late 19th century, French gradually replaced Chinese as the official language in education and government. Vietnamese adopted many French terms. Until now, if we find some old persons in Vietnam, they can speak French very fluently. Especially, in Cambodia and Vietnam, we still use a lot of same words that have origin from French. In addition, many Sino-Vietnamese terms were devised from Western ideas imported through the French. However, the Romanized script did not come to predominate until the beginning of the 20th century, when education became widespread and a simpler writing system was found more expedient for teaching and communication with the general population.
For Cambodia, the Khmer script is used to write the Khmer language which is the official language of Cambodia. It is often considered to be the longest alphabet in the world. The Khmer alphabet is descended from the Brahmi script of ancient India by way of the Pallava script, which was used in southern India and South East Asia during the 5th and 6th Centuries A.D. The oldest dated inscription in Khmer, found at Angkor Borei in Takev Province, South of Phnom Penh, dates from 611 AD. 
The Khmer alphabet closely resembles the Thai and Lao alphabets, which were developed from it.
The Khmer alphabet has fewer symbols for vowels than the language has vowel phonemes. To account for this, each consonant belongs to one of two series, and the vowel is produced depending on which series the consonant belongs to. Therefore, most vowel signs have two possible pronunciations, depending on which series the consonant belongs to. When no vowel sign is present, usually the inherent vowel of the consonant is used. Vowels signs can be divided into two groups: dependent vowel signs, which are written around a consonant letter, and independent vowel letters, which can stand alone. Dependent vowel signs are used more frequently than independent vowels and all independent vowel letters can be phonetically rendered with a dependent vowel. Khmer also has a number of diacritics, which can change the series of the consonant or the pronunciation of the vowel. Cambodian use Khmer language as the major language. Besides this, English and French are used by Cambodian as the secondary language. French and English are compulsory foreign languages in high school as well as in the universities. Here we can analyze the affection of French to Vietnam and Cambodia in script and language. Of course English is the popular language in the world, but French is also a secondary language in Cambodia just due to the period of colony of French for a long time in Vietnam and Cambodia.
For Laos, after the unification of the Lao principalities in the 14th century, the Lan Xang monarchs commissioned their scholars to create a new script to write the Lao language. The scholars probably modeled the alphabet on the Old Khmer script, which was based on Mon scripts. The Lao script is derived from the Khmer script, which explains the similarities between the Lao script and the Thai script. However, since the spelling reform carried out in the 1960s, the modern Lao script is more concise and more phonetic than the previous Lao script and the Thai script.
The Lao language is descended from Tai languages spoken in southern China and northern Vietnam nowadays. The standard Laos language is used in Vientiane and become the national script. A large of emigrant after the wars added local language that is being used as the popular language in Laos.
In general, although three countries have different language and script’s origin, due to the colony of French, they also have the same affection. French becomes the secondary language or the main foreign language in three countries. It also makes their culture becoming popular and diverse.