Birth to a Vietnamese parent creates Vietnamese nationality. Birth in Vietnam alone to two foreign parents is not general jus soli.
Sources: Vietnam Law on Vietnamese Nationality 2008 (English)
A spouse of a Vietnamese may be naturalized without meeting the five-year residence, language, or means conditions.
Sources: Vietnam Law on Vietnamese Nationality 2008 (English)
A child of a Vietnamese citizen parent is Vietnamese under the Nationality Law.
Sources: Vietnam Law on Vietnamese Nationality 2008 (English)
Adult foreigners may apply after five consecutive years of permanent residence, with language, livelihood, and character conditions. Applicants generally renounce prior nationality. Grant is discretionary.
Sources: Vietnam Law on Vietnamese Nationality 2008 (English)
Persons with special/meritorious contributions to Vietnam, or outstanding talent (science, economics, culture, arts, sports, healthcare, education), or whose naturalization benefits the State, may naturalize without the five-year residence, Vietnamese-language, or means-of-living conditions, and may keep their foreign nationality with Presidential approval.
Sources: Vietnam Law on Vietnamese Nationality 2008 (English)