The following languages are available for Nitro PDF Pro: English, French, Italian, German, Spanish, and Dutch.
During the installation process of Nitro PDF Pro, one has the option to set their language of preference as seen below.
After installation of Nitro PDF Pro, one can switch the language of the User Interface by navigating to the 'File' tab and selecting 'Preferences'. Within the Nitro PDF Pro Preferences Dialogue Box, please select 'Language' from the left-hand side navigation pane and then select the Language you wish Nitro PDF Pro to display in. 
For more information regarding how to use Nitro products, please visit the following website for all our online resources: https://www.gonitro.com/support