New messages

I understand that you want those messages to be translated here via Special:Translate and reach Wikimedia wikis in the end, correct? That's not possible unless the message is added by some MediaWiki extension. You could ask that the message be added to the WikimediaMessages extension, but I can't promise you'll have any satisfaction.

The most recent incarnation of this feature request on Phabricator is phabricator:T156210.

A variant of the current practice, which involves editing a MediaWiki:....js page on some central wiki like Meta or Commons, would be to add your localisation to some Intuition tool and then load the JSON file from Tool Labs (if the load is acceptable, which should be possible for AjaxRC).

Can you tell me the exact page where I can ask that?

There is no request page for any of that. You can ask on the issue tracker, on the local admins' pages and on GitHub respectively for the three options.

https://phabricator.wikimedia.org/T164101A request created