Welcome to the community!
I've not done this myself, but there is an excellent series of articles on this here > Segmentation and Snippets - Marketo Docs - Product Docs https://docs.marketo.com/display/public/DOCS/Edit+Snippets+with+Dynamic+Content
As Joe pointed out you can achieve this using snippets as part of your footer. We do it the same way.
Let me know if you need any details.
Keep in mind that if you do decide to add the unsubscribe footer using a snippet instead of using the default Admin > Email footer, you'll need to ensure that those snippets get added to every email you send it. You must legally have an unsubscribe option in any marketing email that goes out.
You may also want to go further with
- Language/Region Segmentations
- Regional/Country Templates
- Localized Forms.
I wrote about this recently: