Indonesia is a multicultural country with hundreds of local languages used by Indonesians with Bahasa Indonesia as a national language and used by the mass media, in formal conversation, at all levels of education, and in written language. This study aimed to investigate whether speaking Bahasa Indonesia in public and at home or not, and whether speaking only Bahasa or besides Bahasa (another language) affects the performance of seven cognitive tests when the assessment was done in Bahasa Indonesia. In case (...) large effects will be obtained, this may demand different norm referenced scores. Data of 840 subjects, in age ranging from 16–80 with various levels of education from six regions were included. The results showed that there was a small disadvantage in the Digit Span for people who do not speak Bahasa Indonesia in public and a small advantage of speaking besides Bahasa (another language) in public on Rey’s Auditory Verbal Learning Test and on time to complete the Figure Reproduction tests. Other tests, such as the TMT, Stroop, 5PT, and Bourdon were without any effect. It can be concluded that corrections for the normative data, as is commonly done for education, age and sometimes sex, for people who do not speak Bahasa daily and for speaking besides Bahasa (another language) considering that the differences were only small, is not indicated. (shrink)