Let's assume that your site is currently using the default language - English - and you want to add another language - Danish-. See below the necessary steps for adding the second language:
From the Translations (Admin Control Panel -> Site Content -> Translations) menu click on Create Translation:
The next screen will show you the Locale menu. Scroll, select the desired language and click Create:
You will return to the Translations menu where you will see the Danish option. To access the file you'll have to download it on your PC.
The downloaded file can be opened with an gettext program. We use and recommend Poedit. The file contains the site's content, and you are free to select the most suitable translation suggestions. After translating the file and saving it on your PC, please use the Upload option. You will see the following screen:
Please upload the saved .po file and the .mo file created by Poedit (you'll find it in the same folder).
You'll return again to the Translations screen. A message will be displayed confirming the successful upload of the files. Now, you'll have to assign a label and click the Active checkbox and then Update for the language to become available in the Front End.
In the Front End the new language will become available for selection in the right hand corner.