I work in a multilingual region, like many of us. My clients' websites are multilingual (often, there's a main language and sub-languages). When I perform a tree test on their structure, is it enough to test on main language or should I test for every language, since translation and cultural habits might come into play?
You need to test every language:
In general, multilingual website should be considered as many localized websites and common test procedure should apply for each of them.