Why do so many bi- and multilinguals feel different when switching languages?

Is the feeling of difference experienced by many bi- and multilinguals linked to a later age of onset (AoA) and a lower level of proficiency in the foreign language (LX)? This empirical study, based on the qualitative and quantitative data from 1005 bi- and multilinguals, suggests AoA is unrelated to feelings of difference. While several participants mentioned the fact that limited proficiency in the LX made them feel different, no statistically significant relationship emerged between the amount of difference experienced when shifting languages and self-reported proficiency in speaking the LX, nor in frequency of use of the LX. The only independent variables to be linked to feeling different were education level, age and anxiety in speaking with colleagues and speaking on the phone in the second language and third language, with higher levels of the latter being linked to a stronger feeling of difference. Some participants presented unique explanations, linking feelings of difference to conscious or unconscious shifts in behaviour and to unique contexts of language use. Several participants also reported these feelings of difference to change over time.