Below article explains key moments how O365 sites are presented to user with different translations.
Fact 1: Each O365 site has Default language (the one it was created in) besides which you can choose alternate language(s) (Site Settings -> Language settings).
Fact 2: Each O365 user, browsing sites can have the preferred profile language.
Fact 3: Each Browser can have the preferred language.
After alternate language(s) for a site is chosen, O365 uses one of the following rules to determine the language in which to display content to the user (see reference):
Example 1: O365 user has preferred profile language and O365 site has this language as default or alternative = O365 site is displayed in user's preferred profile language, i.e. site is opened under according locale, e.g.
it-IT for Italian.
Example 2: O365 user has preferred profile language but O365 site hasn't this language as default or alternative = O365 site is displayed in O365 site's default language, i.e. site is opened under according locale, e.g.
en-US for English.
The language translation feature, which allows to translate our Apps to any, available in O365 site, language, was introduced on September 29 2015.
NOTE 1: Current locale of the site you can find out from the address bar when you open our App's settings. e.g.: https://scorm.365.systems/Pages/Admin/Language.aspx?SPHostUrl=https:%2F%2Fefisuppor1.sharepoint.com&SPLanguage=it-IT&SPClientTag=0&SPProductNumber=16.0.4404.1214&SPHostLogoUrl=https:%2F%2Fefisuppor1.sharepoint.com%2F_layouts%2F15%2Fimages%2Fsiteicon.png
NOTE 2: Locales and languages dictionary can be found in the following article, see column LCID string.