The article is devoted to the issue of word-formation motivation, which does not lose its relevance and plays a role not only in disclosing formal-semantic relations between words of one language and has not only theoretical, but also applied significance. The authors consider word-formation motivation consistently in its varieties in a comparative way on the materials of so different languages as Russian and Arabic and approach the mechanism of achieving semantic equivalence of translation. To the greatest extent, word-formation activity today, due to objective reasons, affects some special branch (technical, medical, etc.) vocabulary, which is increasing from year to year in national dictionaries. This extensive material, selected by the authors, not only illustrates the current trends in word formation in modern languages, but also provides an answer to the question about the degree of equivalence of this subgroup of words in Russian and Arabic. The goal to compare word-formation motivation according to a number of criteria in different-structured languages made possible not only to obtain theoretical information about what features each of the languages has in word formation and what derivational potential it has, but also to reveal an algorithm for translating derived words from one language to another. For this, the authors complete a number of such particular tasks as highlighting significant elements in the neologisms of the Russian and Arabic languages, establishing standards for the formation of scientific and terminological vocabulary in Arabic, searching for tools (transformation operations, specific word-formation formants) that will contribute to the achievement of translation equivalence from Russian to Arabic, etc. Also the analysis of differences in the mechanisms of the formation of new vocabulary in the Russian and Arabic languages provided an opportunity to supplement the relatively young and rapidly developing private methodology of Russian-Arabic translation.