The diaries of Olga Ivanovna Davydova (1813/14-1876) are located in the Scientific Technological Library of Novosibirsk. Amongst 20 copybooks, five are in French. They were written between 1830 and 1848 and relate the travels, the family life and the religious feelings of the young woman in European high society. This chapter presents the level of correctness of her use of the French language, her typical errors and transcoding markers between French and Russian, with some elements of other languages. Its conclusions are that the people from O.I. Davydova's social circle were not used to language switching and their level of French, but also English and German, was quite high, not only because of early learning (the so-called 'gouvernante method') but also because of lifelong learning, reading and travelling.