A city within a bubble universe.

Citadel from the inside appears to be a massive sphere. The city stretches far out, but instead of a horizon, it curves upwards, and if you look straight up you can just make out the buildings far away on the other side. This isn't recommended though, since the artificial sun is quite bright.

All Languages

<1 billion.

Citadel has no currency of it's own. However, as a major trade hub between universes, it provides the courtesy of converting all currency traded into the receiver's choice.

Typical laws against violence and thievery, as well as various smaller laws. All laws are enforced by the Defense Grid.

If you can imagine it, it's probably played.

Bubble Universe

All food can be synthesized almost instantly.

Nowhere, sort of. It exists between the veins of time.

Temperate, typically. Different climates can be generated as needed.

Citadel was founded an impossibly long time ago. The official story was that it was founded as a headquarters for the Bureau, but rumors persist that it has a secondary purpose. Since it's founding it has gone from a glorified relay station to the biggest trade hub in the universe. This is because of it's inherent impartiality in all outside political matters.

Not Applicable

There have been attacks on Citadel in the past, but nobody could stand up to their superior technology.
One of the rumors about it's founding says it was built as a bastion during a long war against some unknown enemy, but this is largely discredited.