Add meta tags with links to pages on alternate languages

[php-coder]

See for details:

• http://webmaster.ya.ru/replies.xml?item_no=15326 (in Russian)
• https://support.google.com/webmasters/answer/189077
• https://yandex.ru/support/webmaster/yandex-indexing/locale-pages.html

Technical debt for: #200