If your website has more than one language, every page exists once in the main language (the editor calls it the default language) and can be translated into each other language. The main language decides the structure: which pages exist, in which order and with which layout; a translation provides the texts for one language, and a page without a translation does not exist in that language at all. The editor itself always stays in English, whatever language you edit. Which languages your site has is set up by the person who looks after your website.

The home page of the demo website in German, with the German menu and the language switch English and Deutsch in the header
The German version of a website: visitors choose the language in the header.