install wordpress language pack manually

– Go to translation project page

– Choose wp version, choose locale, go to bottom of the page, choose do you want download .mo or .po file, and hit “export”.

– On your site server, create a new folder in your /wp-content directory called /languages.

– Upload the .mo file to the languages folder you just created.

Thanks to:https://codex.wordpress.org/Installing_WordPress_in_Your_Language