How to add new language into MyBB forum?

I go to
I click "Find Language Packs", i find the language pack and download it on my computer.

In the language pack .zip archive i downloaded, i see:
czech (folder)
czech.php (file)

I open FTP and upload this folder and file to the folder /www/inc/languages (it can be also /home/yourusername/public_html/inc/languages)

Then i return back into MyBB admin area, Languages: /admin/index.php?module=config-languages
I refresh that page and see new language.

Then i go to MyBB admin area, Configuration, Settings, General Configuration (/admin/index.php?module=config-settings&action=change&gid=3)
and i change "Default Language" to my new language.

I refresh my page and i see texts was changed, new language was applied successfully.