Hi,

1a, Setting WordPress in your language: Admin page to Settings > General > Site Language and select from the list of available languages.

1b, Download installation and active Loco Translate plugin: https://wordpress.org/plugins/loco-translate/

2, In Admin page -> Loco Translate -> Themes -> Translate your theme: 

3, Create new language (your language):

4, Choose language you want to translate into:

5, Loco Translate plugin will automatically generate your language file and save it in the languages folder in your theme ( wp-content/themes/archi/languages/ ):

6, Translate text in default language (English) in your language:

7, Results after translation:

7a, BackEnd:

7b, FrontEnd (comment box on single post): 

You may also be interested, translate the custom post type plugins with Loco Translate plugin: 

Thank you