Lokalise supports over 400 languages, however you can configure your language ISO code as you prefer.
There are two options to change language code.
Option 1. Use language settings
If you would liket to make a global language code change, use this option.
Navigate to projects dashboard, click three dots near language name and choose Language settings... from the dropdown menu.
Option 2. Use Download settings
You can overide global language code setting for each of the export file formats.
Navigate to Download project page, select desired format and adjust language code in the list on the right side. Once adjusted, click Generate bundle to save the preferences.