Learn Survival Vietnamese
Wikitravel users have collectively created a free Vietnamese phrasebook with the goal of making it possible for travelers to "get by" while traveling in areas where Vietnamese is spoken.
Wikitravel phrasebooks are available in many languages and each one varies in depth and detail. Most of the phrasebooks include a pronunciation guide, a general phrase list, information about dates and numbers, a color list, transportation-related phrases, vocabulary for shopping and phrases for eating and drinking. Some are even more in depth, and all are free!
From Website
Vietnamese (tiếng Việt, or less commonly Việt ngữ) is the national and official language of Vietnam. Vietnamese is one of the most spoken languages in the world, with around 90 million native speakers. It is the mother tongue of 86% of Vietnam's population, and of about three million overseas Vietnamese. It is widely spoken in places where the Vietnamese have immigrated such as the United States and Australia. It is also spoken as a second language by many ethnic minorities of Vietnam.
Vietnamese is a Mon-Khmer (Vietic) language, part of the Austroasiatic language family, of which it has the most speakers by a significant margin (several times larger than the other Austroasiatic languages put together). Much of Vietnamese vocabulary has been borrowed from Chinese, most notably Cantonese, especially words that denote abstract ideas (in the same way European languages borrow from Latin and Greek), and it was formerly written using the Chinese writing system, albeit in a modified format and was given vernacular pronunciation. As a byproduct of French colonial rule, the language displays some influence from French, and the Vietnamese writing system in use today, called "chữ Nôm", is an adapted version of the Latin alphabet, with additional diacritics for tones and certain letters.
Vietnamese grammar is very simple: nouns and adjectives don't have genders, and verbs aren't conjugated. Vietnamese is a tonal language; the meaning of a word depends on how high or low your voice is.