Machine translation (MT) serves as a fast way of transmitting web information across countries and MT performance can be highly improved by adapting the source text using a controlled language (CL). Drawing on Halliday’s register-specific accounts as the theoretical framework, this paper investigates multi-faceted adaptations that undergo in the controlled cultural writing (CCW) considering the three dimensions of a language activity, such as field, tenor and mode. By analyzing 296 controlled sentences adapted from 22 folk cultural texts of online Encyclopedia of Taiwan, along with their corresponding good/excellent-level English machine translations, as a case study, this paper identifies some register-specific rules for adaptations. The findings show that variation in grammatical adaptations in CCW, related to the linguistic differences between English and Chinese, supports the mode of online MT application. The paraphrasing of all cultural references for clear transmission of cultural information helps achieve the function of intercultural communication (field), and the conversion from a heavy into lighter context meets western audiences’ pragmatic expectations (tenor). Above all, the MT-driven adaptations in CCW are performed within a context where the interplay of complex factors, such as the function of intercultural communication, cultural inadequacy of western audiences, and MT operational constraints, are taken into account for the creation of readable, scannable cultural machine translations to serve western audiences.