Hi @paulcityhopper,
Currently, if a custom field is set to be mandatory, it should be added to all your forms. Our suggestion is that you create a checkbox with both languages and then an HTML field with a link to a page also written in both languages.
For example, if you want to have English and French Opt-in:
1. Create a checkbox custom field with the text “I agree / Je suis d’accord” and set it to mandatory;
2. Create an HTML custom field linking to a page with a Privacy Notice in both languages (this field doesn’t need to be mandatory since it doesn’t require any action).
What do you think? Would that work with you?