language settings in Office365

Hallo,

I want to understand the language settings in Office365. Is there a deep dive into the language settings in O365? Or on SharePoint online?

How I can change the language and which influence has this change (administrator on tenant side, in user profile, on site, in browser, office and windows language,…)? How index the search? How can a User with German find a document/information which is tagged in English? ….

Regards

Stefan