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Update here. Long story short, you need to upgrade to All-in-One SEO Pack Pro to allow translation of meta fields. Our implementation is somewhat complicated, with the aim being to make the workflow for our translators as easy as possible. We use a self-hosted server running Weblate to manage string translation (both for our websites and for our product). On the Wordpress site we use a customised version of the WPML plugin. Things got complicated when exporting strings from WPML and importing to Weblate – talking to the sys admin who implemented it, the meta fields from All-in-One SEO were even trickier to get working. In any case, all working now Keep any eye out for our site update coming soon here: https://vivaldi.com If anyone out there runs into this issue and needs details feel free to get in touch.

Someone from Moz will probably give better insights but the DA metric may not be impacted by your change but rather the update to the tracking index from Moz. If you read into the DA metric they provide I believe it is relative to their index and will fluctuate based on data they hold - primarily about links and site quality as a whole. I'd be surprised if pruning your content put you in a place where DA was negatively impacted as a direct result.

Jon, If there is no content and these pages are just the download link then instead of putting a canonical link on them, set them as noindex.  I assume you have a landing page that directs people to your downloads, this is where you should optimize your content to get organic traffic, the direct download pages (with 0 content) will have no real value from a search perspective.