To add multiple language support to an existing Rhino 6 installation, follow these steps:
1. In Windows, open the Windows Settings/Control Panel, and click Apps/Uninstall a program.
2. Find Rhino 6 in the list and click Modify.
3. In the next dialog, click the Modify button.
4. In the next dialog, click the Select languages button.
5. Select the languages you want to install and click Close.
6. Click Install Now. The installer will download the language pack. Internet connection is required.
7. Start Rhino and go to Tools > Options > Appearance. Select the language that you have just downloaded and click OK.