For all of our regular accounts (Basic, Pro & all Growth Plans - annual and monthly) you can only set one language.
If you want two languages you need to sign up with our Agency Accounts that enables you to have two clients and set two different languages for both. i.e. One client is English and one client is French.
If you have more than one language that you want to run your campaign in you can upgrade to a higher Agency plan that allows for more clients. Please email firstname.lastname@example.org to learn more about our Agency Accounts and Plans.