Gaia Vince for The Guardian:
In the 1960s, one of the pioneers of psycholinguistics, Susan Ervin-Tripp, tested Japanese-English bilingual women, asking them to finish sentences in each language. She found that the women ended the sentences very differently depending on which language was used. For example, ‘when my wishes conflict with my family... ’ was completed in Japanese as ‘it is a time of great unhappiness’; in English, as ‘I do what I want’. Another example was ‘real friends should… ’, which was completed as ‘help each other’ in Japanese and ‘be frank’ in English.
From this, Ervin-Tripp concluded that human thought takes place within language mindsets and that bilinguals have different mindsets for each language, an extraordinary idea but one that has been borne out in subsequent studies; many bilinguals say they feel like a different person when they speak their other language.
The article is interesting throughout.