Just the straw that finally broke the camel's back . . .
Additionally, on the positive side, some people want to contribute to a project and wish to do so in a certain language. This could be because it's their preferred language, or they may want to exercise a newer skillset or build a contribution portfolio in a new area.
The language doesn't matter much in a pre-compiled application, but when it's an open source application looking to gather and foster a community or build momentum, the language does matter.
I'd speculate the main reason people write things like that, and so prominently, is because they hope it will attract contributors who either already know that language or are enthusiastic enough about it to progress the project significantly.
Otherwise someone may just pass it over assuming it's another piece of junk written in <insert-your-least-favourite-language-here>.
Some things I found:
1. You have a much better chance of getting upvotes if you appeal to a popular technology. Had I not mentioned Meteor I suspect I would never have made it to the front page.
2. In my case, most of the initial interest came from those more interested in the underlying technology than the application.
3. I found it very difficult to market the project as an issue tracker as it was already established as a meteor project.
Could not get it to run. Broken with current meteor?
I'm a long-time Emacs user, but have been growing increasingly tired of it. Whichever incarnation of Emacs I turn to, it just seems old-fashioned and outdated. And yet, whenever I try another editor, I end up coming back to Emacs. And one of the reasons is often the language (or ability at all) with which to extend it.
They don't, but they're not 'talking' to users with those statements. For Open Source projects getting contributors is just as important as getting users, and they care what language you're using. Especially on a site like this one there is a decent chance that you can reach people who also want to help out with the development.
For languages like Go and Rust which compile to native code, I don't give a damn -- except to note that it is such a language.
For other projects (like this one) I find that the language can be a distraction from the actual value it provides.
[1] https://medium.com/@raphlinus/inside-the-fastest-font-render...
Sublime Text was horrible in that it offered an easy refuge to many young and inexperienced people. But ultimately it was a closed source prison that they got pulled into. And yes, I'm a professional developer having founded multiple companies. I'm a capitalist, nothing wrong with selling software. However, having great tools that last a lifetime available is one of the most important point I learned and like to teach to my students (I'm a lecturer, too). Why lock yourself in? Just because it looks more shiny and is easier in the first week? That's a good reason to use many things, but not your primary driver as a professional software engineer.
Hooray for these new editors that look shiny and are open source. And then when the students ask how I did those crazy things in Emacs, they still get those huge eyes and want to gobble all the information in. This kind of curiousness happens rarely with people locked into proprietary systems.
In an open source project, it matters to potential contributors. It might matter to users in terms of what platforms it can be ported to - probably less these days, where "portable" means "runs on Windows, Mac, Linux", but still, it is not irrelevant.
You can write bad/poorly optimized code in any language. But its a lot harder to write polished, efficient, low consumption applications in an electron stack for some application types than it needs to be.