problem with editing the content

Hello,

i would like to translate/edit the content of my site, but nothing happens.

I have written in Russian, and the information on the site is displayed in English.
When I choose during installation the function multilingual site, the home page does not look right (see pic)

During installation you have selected a language that is used by elements common to all templates and administrator. But template has its own texts, also if quickstart was used - provided content is in english.
From what I see you need to edit menu to translate them to your language. Also template language file should be edited.

I can not choose the language I want and I can not add it to the language of the content. I had to choose during reinstalling function of the two languages for the site.

Joomla allows to add languages after installation. Perhaps the problem was somewhere else?

Joomla allows to add languages after installation.

Yes, but it didn't add them to the language of the content((

Because as I have written - it is a sample content and it is only in english. You still need to replace sample content with your own one.