Written in 1095/1097 by Philippos Monotropos, the Dioptra represents a work of app. 7000 political verses consisting of five books: the Klauthmoi, a poem of contrition addressed to the soul, and four books of a dialogue between the soul and the body treating various theological and philosophical issues. The Dioptra was immensely popular throughout the Byzantine and Post-Byzantine periods. One of the reasons for this popularity was doubtlessly its language and style, which appealed mainly to a literate, though not scholarly public: a simple Schriftkoine with elements of unclassical grammar and syntax. Occasionally vernacular expressions are used as a stylistic element, while figures of speech are applied rather rarely. In the second quarter of the 14th century the work was translated into the Middle Bulgarian redaction of Church Slavonic. The abundant manuscript tradition – presently we know about 200 Bulgarian, Serbian and Russian manuscripts containing either the complete Slavonic Dioptra or parts of it – attests its enormous popularity among the Orthodox Slavs. In the present paper author examines data from orthography and phonetics and compares the language of the Greek and the Slavonic version with special regard to the translation technique.