Livegrade offers the possibility to change the language for the User Interface independently from the setting for Mac OS X.
To do so open the preferences. Go to the Main Menu and choose “Livegrade > Preferences…”. In the “General” tab of the preferences you will find the section “Language” right at the bottom:
The dropdown lets you choose between automatic selection based on the system settings of macOS, or force a specific application language.
After changing the settings Livegrade will show an alert asking you to restart the application for the changes to take effect.