К какому веку относят первые найденные письменные источники на русском языке?
Up to the 14th century, ancestors of the modern Russians (who likewise called themselves "ruskiye") spoke dialects of the Old East Slavic language, related to the dialects of other East Slavs. This spoken tongue and the literary Old Church Slavonic language operated throughout Kievan Rus. The earliest written record of the language, an amphora found at Gnezdovo, may date from the mid-10th century. (Until the 15th century, Gnezdovo was a part of the independent Principality of Smolensk.)
10th