My understanding is that for most of Chinese history the standard language was usually that of the capital, which of course shifted from dynasty to dynasty. Sometimes the common language was the language of the capital of a recently extinguished dynasty. For example, for a long time after the fall of Luoyang in 311 to northern non-Chinese peoples, the nobles of the southern state of Jin (centered on modern day Nanjing) continued to speak the dialect of Luoyang.

Whether a common language existed in earlier times, say the time of Confucius (5th century BC), is the subject of debate, but the standard view is that there was a common language and it was called the 'elegant language' 雅語, the language of the capital (Luoyang), in contrast to the 'everyday language' 俗語. So a small portion of the people of that time might have been able to converse with people of another locality in that language, and may also have recited poetry and sang certain ritual songs in that language.

Sources: Mather, "A note on the dialects of Loyang and Nanking during the Six Dynasties" Wilkinson, 'Chinese History: A New Manual', fourth edition.