We don't tend to "reuse message" in other context... So I don't think we necessarily need to "care" about about reuse.

I don't think they count as "temporary" either.

It seems fairly reasonable to add a new i18n subfolder. Needs a little bit of work from the translatewiki.net side and config, but nothing to worry about.

Need to decide on some qqq messages too, but they could be fairly generic to mention they're in the used in the Tech News.

@Reedy Thanks! I think the only open question is then:
Is it feasible to easily solve the challenge of strings-with-embedded-variables?
i.e. list (B) which needs to have weekly and annual changes to the 2021/33 part in each, but is otherwise static.

Yes, it’s feasible, MediaWiki messages can have parameters:

Latest '''[[m:Special:MyLanguage/Tech/News|tech news]]''' from the Wikimedia technical community. Please tell other users about these changes. Not all changes will affect you. [[m:Special:MyLanguage/Tech/News/$1|Translations]] are available.

but they need to be specified each time they’re used (e.g. {{int:messagename|2021/33}} here), so it’s not practical to keep the translation variables used in the current page translation mode.

Change 748773 had a related patch set uploaded (by Jon Harald Søby; author: Jon Harald Søby):

[mediawiki/extensions/WikimediaMessages@master] Add messages for the Tech News to a new message group

https://gerrit.wikimedia.org/r/748773

Change 748776 had a related patch set uploaded (by Jon Harald Søby; author: Jon Harald Søby):

[translatewiki@master] Add Wikimedia Newsletter group from the WikimediaMessages extension

https://gerrit.wikimedia.org/r/748776

How is this planned to be used? int follows user interface language, while page translation follows page content language. Using a mix of both leads to worse user experience in my opinion.

I agree with @Nikerabbit that we shouldn’t mix page and UI language (as I’ve already expressed on Meta), and still hold that T272102: Support substituting templates in MassMessage-delivered messages for cross-wiki messages should be fixed instead, so that we could just use Meta templates in the newsletter.

I think implementing a magic word similar to int but one that follows page language could also be possibility and likely easier than T272102: Support substituting templates in MassMessage-delivered messages for cross-wiki messages.

That’s definitely better than using the UI language, but still more limited than allowing substitution of arbitrary templates: I’m not sure whether we’ll ever have an email address obfuscating template in WikimediaMessages, but even if we will, I don’t think a code like example{{intp:misc-email-obfuscation}}wikimedia.org instead of example{{@}}wikimedia.org will be used a lot; translatewiki.net is still a third-party service with separate registration and separate aggregate groups; and translation variables still (by custom) work differently in MediaWiki messages than in page translation.

Change 748773 abandoned by Jon Harald Søby:

[mediawiki/extensions/WikimediaMessages@master] Add messages for the Tech News to a new message group

Reason:

Not much interest, can resurrect if anything happens.

https://gerrit.wikimedia.org/r/748773

Change 748776 abandoned by Jon Harald Søby:

[translatewiki@master] Add Wikimedia Newsletter group from the WikimediaMessages extension

Reason:

Not much interest, can resurrect if anything happens.

https://gerrit.wikimedia.org/r/748776