Language and speech occupy central place in early cognitive development, constituting the basis for reading and learning. International science has produced a number of diagnostic paradigms as well as a conception of developmental psycho-linguistics. At the same time there is a lack of diagnostic techniques for assessing development of language and speech in national science. The paper describes procedures for adaptation of the technique Preschool Language Scales 5th Edition; PLS-5 which is used in clinical practice for assessing a child's language competencies if there is a suspicion of retardedness. The technique has proved its effectiveness for various groups of children, normal and otherwise. The paper contains all modifications introduced by the authors in the process of translating the text into Russian. Effectiveness and reliability of the technique were assessed with respect to a case study of a bilingual child who completed the test in English and then in Russian. The results demonstrated a high degree of compatibility of the data obtained with the help of the two versions of the technique. On the whole the results demonstrate that the Russian language version of the technique can be used as a reliable and valid instrument of diagnosing speech development in monolingual and bilingual children. We expect that application of the technique to large numbers of Russian-speaking children will help to improve its psychometric parameters and discover norms to be used in diagnostics.