1. Indonesian culture is directly descended from the rich Malay culture that permeates the entire Malay Archipelago, a culture that has given rise to countless kingdoms and sultanates, a rich literary language (Jawi), arts (batik making, wayang kulit, kris-forging).
While it would be the only Malay civ in the game if included (which itself is reason enough to include them given the size of this ethnic group), doesn't this combine a few traditions from outside the core Indonesian region? Kris are of particular significance in the Malay Peninsula, which existed mostly as independent kingdoms throughout the Majapahit period, so this is at least a shared tradition (as is batik).
2. Indonesia's status as the source of the spice trade drove the Age of Exploration by the Portuguese, Spanish (Magellan) and the Dutch. The spice must flow; and it came from Indonesia.
It came from Indonesia, but mostly reached European markets via India and China.
Linking the Srivijaya/Majapahit to modern Indonesia is in fact far better than linking the Celts to modern Scotland
Nearly anything is better than linking the Celts to modern Scotland...
Javanese and Malay are very much living languages, unlike Gaelic.
Gaelic is a living language, just not one that's closely-related to historical Celtic languages of the period represented by the game's Celts.
Also, the Zulu were probably added due to the support of the fans rather than for the sake of the expansion.
This has been confirmed in interview; we've been told that about a third of the civs selected were chosen because of fan interest, with the Zulus given as a specific example. It's not yet clear what the other two are - Assyria and Poland are possibilities, but both can equally well be argued to relate to expansion themes. The Native American civ is probably one of the others, since it's otherwise unclear how Native Americans fit into BNW's themes. The third could well be an unrevealed civ.
There are many accepted names for it but I dislike "Malay Archipelago" because it implies Malaysia is the largest chain of islands.
The term "Indonesian Archipelago" is the one I personally believe - and strongly believe at that - people should be using.
I prefer "Malay Archipelago" if only for its historical resonance for exploration and natural history, although the term seems to have fallen into disuse. The "Malay" of the name predates the use of "Malaysia" (and possibly "Malaya") and accurately describes the dominant ethnic group throughout the islands - if anything it's Malaysia that's misnamed since the majority of Malays live in Indonesia.
Biogeographically, "Sundaland" and "Wallacea" are current usages but both are required to describe the archipelago as a whole (and Sundaland still extends into the Malay Peninsula).
The generally accepted modern regional name appears to be Indo-Malaya, although again this encompasses more than simply the archipelago, encompassing all of Sundaland (including the Malay Peninsula) and all of Wallacea (including New Guinea). In marine terms, the Indonesian archipelago + the Philippines are also called the Coral Triangle. Tectonically they also make up the major part of the "Ring of Fire".
The only available name for the main island group itself is, of course, Indonesia ... which would annoy people in Brunei, Sarawak, Sabah, the Philippines, Timor-Leste and Papua New Guinea (and likely Aceh as well).
Really, I think Malay Archipelago remains the best option, since it's specifically confined to the island group and covers the entire territory.
