LightHeaded, EveryQuest, TourGuide are great addon but none of them provide their data in other language than English.
Instead of doing an addon that would contain all the data they need why not give addon author access to a data repository which contain all basic quest data. They can then choose which data to use and which format to store the data in their addon.
If you would like French language data, just ask Wowhead for it, or for permission to mine it and distribute it.
Or you could ask Curse/WowDB; they appear to have a French language option. (I'm unsure if they actually have French data, though.)
I really see no point to having a lib for this. If there was a need, a lib would have been made. More specifically, there's no need for a common format... if an addon needs to mine the data, just do it for yourself.
Yes, because what I really want is each of my half-dozen addons having something at all to do with quests loading its own unique database of info on 14,000 quests into memory.
Thought I'd chip in, I'm kandarz, author of EveryQuest.
Just committed a 3.3 compatible version that includes QueryQuestsCompleted() importing.
I've tested it pretty well but let me know of bugs on the ticket manager.
Importing 2300 quests took about 30 seconds on a decent computer (2ghz, 4gb). When you import, you'll most likely get a red notice in your chat log about not having some quests in the db. These are special things even WowHead doesn't display (they're there but you have to use the quest id in the url).
But that's why they do it that way (I believe). If you did change factions, it would be marked as completed automatically. It helps Blizzard. So this is something addon authors will have to take into consideration: for quests that are both horde and alliance, they both get marked as completed if you do them. And vice-versa: if an addon wants to tell a player which quests (s)he hasn't done, it needs to be filtered by faction.
There are quests which exist for horde and alliance, the only difference is the questgiver and the achievement they count for often.
If i did the horde-one i also fulfilled the alliance one it seems.
No this char has been horde since its creation, so it cant be the factionchange.
Can you give an example? I've seen a lot of duplicate horde/ally quests, where the objectives are the same and sometimes even the quest text is the same, but the questgivers are different. In each of these cases, the two quests had different IDs... so what's the output of the API look like for you?
 = true, Mission: End All, Be All : Nazgrel at Thrallmar in Hellfire Peninsula has asked that you slay Arazzius the Cruel.
 = true, Mission: End All, Be All : Force Commander Danath Trollbane at Honor Hold in Hellfire Peninsula has asked that you slay Arazzius the Cruel.
is what i got in my savedvars file where the returnvalue should be properly saved
It's not a 100% correlation though. For example, these two quests have the same rewards, but you kill different targets: http://www.wowhead.com/?item=31719 The API only reports that I completed one of them.
Is the QueryQuestsCompleted Account bound or just character bound?
Thinking they added this for something other than just to please addon devs.
Complete every quest for every race achievement. Reward: "Stick"