Menu Planner 2 follows your device’s language. It’s available in English, Spanish, French, German, Portuguese (Brazil) and Italian, and so is Help & FAQ.
To use a different language just for Menu Planner 2, tap your picture at the top left, then Settings → Language. That takes you to the Settings app, where you can pick one.
Don’t see Language on Menu Planner 2’s page in the Settings app? Add the language to your iPhone first, in Settings → General → Language & Region.