Visual Studio and SolarLint doesn't finish downloading additional languages

First time using SolarLint. I have a bunch of solutions.
The initial time I opened a solution, I get a dialog asking if I want to download and activate additional languages. I accepted, the progress bar reaches 100% but never finishes.
I exited the download window.
It mustn’t have worked because I keep getting prompted each time I open a solution.

Note we’re behind a corporate proxy-firewall which can be a bit zealous.
I saw issue 558 and I tried pinging and it failed…