My impression is that it is just someone who created a community for each language they could think of. But if programming.dev is a popular instance that is well managed, then sure. But for now, it seems that lemmyrs.org have more users and momentum.
EDIT: On a closer look, it turns out my first impression was quite wrong. programming.dev seem like a quite well managed place, so I do not have anything against using that as a base for rust if that is what the rust community chooses.
The new icons look really good, but unfortunately they are not really fulfilling their full purpose. The purpose of an icon is primarily to make it easier to distinguish between different communities in this case. The most noticeable features of these icons are the outer shape and the colour scheme, this makes it easy to distinguish between Beehaw communities and non Beehaw communities (so far so good). But it almost makes it harder to separate between the different Beehaw communities, since that information only resides within the inner symbol of the icon and that is far less prominent than the color and the outer shape. Unfortunately, we tend to think things with symmetry looks better, which makes a good looking icon theme and a usable icon theme a bit orthogonal.
So, while I really like the look of the icons (and how they tie in to the Bee theme of the site), I'm not a fan of the usability aspect of them.