If you are using the new Nitro PDF Pro for macOS, the software does not have an internal language switcher. Instead, it follows your operating system’s language.
If you are using the new Nitro Cloud (the online PDF editor), changing language is different: how to change language in nitro pdf new
The process to alter the interface language is uniform across most recent builds. Follow the steps below: If you are using the new Nitro PDF
Changing the language in the new Nitro PDF is not as intuitive as it used to be, but it is entirely possible. Click Options (or Preferences) to open the configuration
If you are a business user managing multiple licenses, consider deploying the language MST (Microsoft Transform) file via Group Policy to automate this for your entire team.
If you only want to change the language for spell-checking (not the buttons and menus), the process is slightly different:
In this Backstage view, look at the vertical list of options on the left-hand sidebar. You will see items such as Open, Save As, Print, Share, and Protect.