(covers information from several alternate timelines)
Russia was a transcontinental country spanning the Europe and Asia continents on the planet Earth, to which was its largest nation. The capital city was Moscow. Its official language was Russian and was a member-state of United Earth.
In 1917, the ruler of the country, the tsar, was overthrown and replaced by a communist government under Vladimir Lenin. Russia was a communist state until the dissolution of the Union of Soviet Socialist Republics in 1991. (ENT: "Storm Front"; VOY: "Future's End, Part II")
In an alternate timeline, Vladimir Lenin was assassinated in 1916. As a result, the Communist revolution never took place. The German invasion of the country in this World War II was more successful than in the original timeline, succeeding in reaching and overrunning Moscow. However, by the early 1940s, Russians were trying to take back Moscow, which many Germans felt was because they were advancing too far too quickly in their military endeavors around the world. (ENT: "Storm Front")
A 21st century-era political map of Earth was stored in the USS Enterprise library computer in 2254. The location of this country was labeled on this map. it was among the materials viewed by the Talosians when they scanned the Enterprise computer. (TOS-R: "The Cage")
Retroactive continuity: 20th century-era maps of the northern hemisphere Pacific region were stored in the USS Enterprise library computer in 2254. One map depicted the east coast of Asia's USSR nation and Alaska on the west coast of North America. Another map depicted the globe from the point of view of the Arctic Circle, showing the same region. These maps were among the materials viewed by the Talosians when they scanned the Enterprise computer. (TOS: "The Cage")