Hi Lindsay, the best way to do this is to capture the language preference when you capture their email address (add them to your database). You can then make two versions of the email and in your campaign send based on the language preference field.
Alternatively, you could link to "view in french" and have a landing page with the email in french or vise versa.
If you can't capture language preference, another method is to build a language segmentation based on the country where individuals are located. Even if you do capture the language on a form, I would still recommend building a segment as you can use the segment to make any email you send dynamic, as opposed to having to clone the email and configure multiple sends.