Marxism was brought to the Indonesian archipelago by Dutch radicals in the 1900s. The first Marxist journal in Indonesia, Het Vrije Woord (begun in 1915), was published in Dutch. From the late-1910s, however, Marxist newspapers began to be published in Malay, Marx's writings were translated into Malay, and Indonesians started to write book-length works inspired by Marx's ideas. This paper explores how the Marxian language of class was localized in these writings, focusing on how Indonesians explained, transliterated and translated the terms proletariat and bourgeoisie. Sometimes, these terms were kept in their Dutch form or transliterated, often to stress their international nature and invoke the prestige of Marx's 'scientific' system of social analysis. At others, , they were exchanged for vernacular terms which lay beyond Marx's historical-materialist typology of social groups. 'Proletariat' was rendered 'rakyat' (the people) or 'kaum kromo' (the poor); 'bourgeoisie' was swapped for 'kaum hartawan' (the rich) or elided with 'hajji' traders. Moving between an international and a local idiom enabled Indonesians to associate themselves with the international class struggle, , and to speak in a manner that would resonate with local constituencies. There was a tension between these two approaches, however, since the use of Marxist terms could be used by their enemies as proof that they were 'internationalists', and unable to empathize with their fellow Indonesians. In 1933, Sukarno argued that the word 'proletariat' should be abandoned in favour of the more indigenous term 'Marhaen', signalling a turn away from an international language of class.