Even if you don't want mediawiki for various reasons, you can set it up in Wikimedia Cloud. We already hosted Discourse there for years.
Cloud is 1)
not exactly an improvement in terms of privacy, 2) a drag on human resources as it will take significant time of an employee or community member (who is likely unskilled at operating Discourse) to keep the site running. If it seems likely that the forum will be around for long, it might be worth moving it to internal hosting (which will be a lot more expensive in relative terms but still not really significant compared to the Wikimedia movement's resources, I imagine). In the short term, just buying hosting while we see how well the new thing works out is a very reasonable approach. Our community's hostility to experiments is one of the biggest obstacles to adaptation and addressing long-present problems (such as using discussion technology that was considered pretty good forty years ago).
No it doesn't, which is why you almost never see multilingual discussions on meta. It "works" in the same sense that two pieces of stick work as a lighter: it can be used for the same purpose with sufficient effort, but that effort is so high that almost no one will use it in practice.
Language barrier is a problem but so is privacy, there is a reason we host everything onsite. For example, I don't know the details of how it uses Google Translate but it is possible we end up sending some data to Google that are either not anonymized or can be de-anonymized easily. Not to mention the cloud provider hosting the website having access to everything and so on. And not to mention auto-translate is not perfect and can cause all sorts of problems in communication.
While that's a good point and something to consider if we keep Discourse around, the current reality is that discussions mostly happen on Facebook, Telegram and Discord, all of which are worse in terms of privacy than a Discourse site hosted by a contracted organization. These discussions remind me of the trolley problem a bit - is it really preferable to let five times more people get run over, just because that way we can wash our hands afterwards and say we didn't officially approve of either option?