Hi,
I am the developer behind the Outlook plugin itself (Sendent) and worked on it ever since the beginning of the Outlook integration.
We recently made the Nextcloud app translateable. That app of course is AGPLv3.
Regarding the Outlook client itself that is not part of the Transifex translations. We still and will always offer a free version. Currently we are at v3 but the feature-set is the same as offered initially in 2017: Secure Outlook add-in is now available for testing in free-as-in-beer version. For now we are keeping that code closed-source.
You might ask yourself then what are the benefits of combining the Nextcloud app (https://apps.nextcloud.com/apps/sendent) with the free version?
The app it firstly meant as a GPO for all the connected clients. The general settings work (language, cursor location, add date to path, debug mode) and at the very bottom you will find the retention assistant. Now this is probably not well documented, but basically it will automatically clean-up all your shares that have expired after an X amount of days. This works with the free versions as well.