In what language should the title and description of a YouTube video be written?

Question

YouTube

I am interested in the target audience of Europe, USA, Australia, India, China, Russia.
In other words, where are the most people?
In what language should the title and description of a YouTube video be written?

Name

Beautiful relaxing music for sleep or meditation

Description

Beautiful relaxing music for sleep or meditation.
Great relaxing music for sleep or meditation.
सोने या द

Duplicate text in 5 languages ​​or write only in English?

Looking through similar videos of American users, I see that the titles of their videos are in Russian, which is strange. And next to it are the same videos of American users, with titles in English.
It’s not clear (Youtube auto-translates? But not everything?)

Answer 1

You designate some language as the main one during the initial filling of the information.
Then in the YouTube video editor - Subtitles - Add Language
and add a new language, it has new Title and Description in the new language.

screen

Users who have one of the languages ​​available in your video selected will immediately see the title and description in that language.

Answer 2

It’s not clear (Youtube auto-translates? But not everything?)

Almost