If Serbia and the Inuits can get their own thread, Vietnam can get one.
Appeal to History: Vietnam has an interesting history that stretches back several thousand years. As a civilization, it could be argued that they exist for this long. However, the Vietnamese have suffered from numerous periods of occupation, particularly by the Chinese. At times, the Vietnamese were under foreign domination, such as by the Chinese or French. However, eventually the Vietnamese succeeded in overthrowing their oppressors and creating their own country. In the process, the Vietnamese often absorbed technology and cultural aspects from their oppressors, combining these things with their own traditions to craft something paradoxically syncretic while uniquely Vietnamese. An example of this can be seen in the Vietnamese religion Cao Dai.
Though the Vietnamese were often forced to stand up against larger foes, they had their own periods of conquest and invasion as well. The Vietnamese people, for example, were eventually able to completely erase the state of Champa from the map, a state that had existed in South/Central Vietnam for hundreds of years. The Vietnamese also had varying degrees of success against their other Southeast Asian neighbors. Civil wars crippled the Vietnamese at times, but in some ways the country benefited from them--the states that vied with one another for supremacy found it prudent to seek foreign aid and innovation. Gia Long, for example, had an arguably cosmopolitan court staffed with Portuguese, French and various Southeast Asian (Cambodian, Thai, etc.) ministers.
In light of its long history, several successful dynasties and unique culture, I am advocating Vietnam's inclusion for Civilization V. People often complain that there are a lot of European civs but comparatively few from other parts of the world. Vietnam has a history that rivals that of the other East/Southeast Asian polities (Japan, China, Korea, Siam).
My ideas so far:
Some assorted other ideas:Vietnam
Leader: Le Thanh Tong
UA: Attrition (Cities do 30% more damage to all non-siege units when bombarding. Workers are built 25% faster and, when stacked, provide a 10% strength bonus. Defeated enemies within or adjacent to Vietnamese territory grant golden age points)
UU: Huochong [Hand Cannoneer] (Replaces the cannon. It ignores movement penalties on tiles that have forests/jungles and does not require set-up to attack. It keeps both bonuses when promoting)
UB: Water Puppet Theatre (Replaces the theatre, but costs no maintenance. In addition, gives +4 culture if the city has a lake or river within its borders.)
Focuses-Vietnam's unique traits focus on exploiting certain tile types. Using terrain effectively will be of greater importance to Vietnam than some other civs. Vietnam will be able to defend itself pretty well if the player makes use of forests and jungles well. The combination of their deterrent UA, possibility for more golden ages and culture improving UB can give them an edge in the culture war too. While they are best suited to turtling and winning via culture, science or some other peaceful means, Vietnam's UU allows them some flexibility in the mid-game.
-The Vietnamese could have a UA that takes into account their history of syncretism, allowing them to mimick abilities of other civs. This was my original idea for their UA.
-The Vietnamese could easily have some kind of modern infantry or artillery unit to take into account their wars against the French and Americans. In my opinion, though, this is not a good idea. It is better to leave modern Vietnam out of the equation in order to avoid angering the large South Vietnamese diaspora/potential consumer base.
-Some kind of jungle UA could make sense for the Vietnamese, I guess.
-The Vietnamese used elephants in warfare, albeit not as much as some other Southeast Asian groups. Some kind of gunpowder elephant unit might be neat, but I think there are enough civs with pachyderms. Also, I'm not sure if the vietnamese ever actually used a combination of elephants and gunpowder weapons, even though both were available to them.
-The Vietnamese could also have fire lances or poison arrows.
UU: Fire Lancer (Replaces the pikeman). Unlike a pikeman, it can attack both indirectly from a distance (like an archer) or engage in melee combat. It has more strength than a pikeman and slightly less than a crossbowman. In addition, it comes with a promotion that lets it avoid movement penalties when moving through forests or jungles.
UU: Fire Lancer alt idea (Replaces the crossbowman. Has a 25% chance of doing a small amount of damage [50% base ranged strength] to any unit, barring itself, surrounding its target. This % chance is calculated separately for each surrounding unit, meaning that every unit surrounding a target has a 25% chance of taking damage rather than the system being "all-or-nothing." Can also damage allies, however, so unit placement is important here.)
UU: Poison Archer (Replaces the composite bowman. Has a 25% chance of poisoning an enemy unit. A poisoned enemy unit will take an additional 10% damage each time it enters combat for the next 10 turns. Elephant units have a 50% chance of being poisoned. The poison promotion continues to crossbowman but vanishes with further upgrades.)
-There are many other respectable Vietnamese leaders throughout history. Le Thanh Tong ruled Vietnam during a particularly notable golden age for Vietnam, however. Ho Chi Minh is a bad choice for Vietnam's ruler: This is not because Ho Chi Minh was terrible per se (he certainly wasn't great though). Rather, Ho Chi Minh is bad because such a choice would alienate the very large number of Vietnamese who live in other countries that had South Vietnamese roots during the Vietnam War. It is also for this reason that I felt a non-modern UU would be more amenable.
The Trung Sisters would be an interesting option for a leader. They are pretty famous, are well-respected and could have humorous diplomatic interactions. They could have opposing personalities in order to make diplomacy with them a bit funnier.
Gia Long isn't a bad choice imo.