Mathematics, as universal language, is used by individuals with different native in a way that is influenced by their native languages. Two kinds of uses, formal and informal, of mathematical language arise since the mathematical statements or sentences can be expressed in a native language by defining the meaning of symbols in that native language without the use of the symbols themselves. Translation from a certain native language to the language of mathematics can be regarded both as transforming sentences from native language to mathematics and, more general, as transforming real-life events to mathematical models. The aim of this study is to investigate transfer skills from informal to formal mathematical language of middle school pre-service mathematics teachers from the USA and from Turkey. In this qualitatively designed study, data were obtained through a written questionnaire and clinical interviews. Research results show that participants from Turkey had difficulties in terms of constructing quantities apart from the difficulties of not recognizing the functional relationship in word problems. On the other hand, the participants from USA had difficulties with transferring informal sentences and statements to formal mathematical language.