Is this limited only to US region? Doesn't work in my phone with Finnish region.

 This feature also gives users the power to translate text from an image to another language. Currently, Live Text works in seven languages – English, Chinese, French, Italian, German, Portuguese and Spanish. This feature is only available for Apple iPhones launched after 2018 or above iPhone XS.

It is not limited by region so the feature should work on your iPhone 12 Pro Max when used to translate of the above mentioned languages.

Axel F.