How to translate theme?
In order to translate the theme, please follow the next steps:
Theme's .pot file is located in /wp-content/themes/your-theme-name/languages folder.
Please use PoEdit - https://poedit.net/ to translate the .pot file and create respective .po and .mo files.
In order to place .po and .mo files properly and not have them deleted when you update the theme, upload them to \wp-content\languages\themes folder. If you don’t have languages folder in your wp-content directory, please proceed and create one. Then create themes folder, and paste the files in it.
Please name .po and .mo files e.g. potname-nl_NL.po and potname-nl_NL.mo (nl_NL is the language code for dutch and potname is the name of the .pot file you have started from - it corresponds to text domain of the theme). For other languages' codes, please refer to the following link: Internationalization.
Alternatively, you can upload the .po and .mo files to your theme's /wp-content/themes/your-theme-name/languages folder. In that case name them only using the language code (for example nl_NL.mo and nl_NL.po)
Also make sure to translate the theme's plugin .pot file, located in \wp-content\plugins\your-theme-name\languages folder.
The steps are the same as for the theme, except the files should be named bt_plugin-nl_NL.po and bt_plugin-nl_NL.mo (with appropriate language code).
For plugin’s .po and .mo files, you should place them in \wp-content\languages\plugins folder.
You can set the site language of your WordPress installation on Settings > General. WordPress will automatically use the right language files if they exist.