[[Special:AdvancedTranslate]] protection
The mechanism is the usual one for wikis. Just watchlist the page and enable watchlist email notifications, tell others to do the same. Works for me. Changes to aliases are exported at intervals of several weeks or months, so there's always time to review the other people's changes.
Can't look into the history now, but please first ask those users why they changed the aliases, let's see. Also note that ideally a discussion about the aliases should happen on portal talk:hi rather than hi.wiki; you can easily open it on both and cross-link so that everyone is aware.
"ideally a discussion about the aliases should happen on language portals..."
Myself, I think that it is best to find the largest community for a particular language/software combination to discuss important changes to a localisation. For MediaWiki software the largest community for any language is usually on its Wikipedia. When a decision is made, it is possible to make a note of the decision on translatewiki.net, linked to the discussion on Wikipedia. You could make notes on the portal talk page, or you could choose to open sub-pages to the portal for localisation notes and styles, linked from the portal page. It is useful to make notes on GRAMMAR, PLURAL, GENDER as well as the aliases, namespace names, magic words and other things relevant to a language.
I couldn't agree more that the best place to discuss important changes is Wikipedia of concerned language (for MW s/w, of course). There should be some level of protection for such pages. Email notification is a good way to keep track, but it's not ideal. I'm afraid that just an email notification won't work because users may forget to check their emails.