Widespread imperial presence leads to the widespread adoption of the empire’s language for business and political purposes. The peak of an empire’s military and economic influence, however, regularly antedates the peak of the imperial language’s ubiquity.
Greek and Macedonian influence arguably reached its zenith sometime prior to 250 BC, but the Greek language would become most widespread a century or two later.
The Roman Empire arrived at its apogee well before 476 AD, but Latin usage, both written and spoken, continued to expand for several centuries afterward. More texts were composed, and more of them have survived, in Latin after 476 than before.
Visually, this phenomenon could be represented on a Cartesian plane. The horizontal axis shows time, and the vertical axis would represent intensity and geographical spread. Something approximating the familiar bell curve would map an empire’s political, military, and economic significance. A second curve, of similar shape, would mark the spread and use of that empire’s language. This second curve would be offset to the right, such that the peak of an empire’s geopolitical importance would occur temporally prior to the greatest spread and use of its language.
The spatial distribution, and frequency of use, of an empire’s language is still increasing when the empire itself is in decline.
The Spanish, French, and British empires were already in decline while the Spanish, French, and English were becoming increasingly widespread.