On April 21, 2020, Google announced that their Prettify syntax highlighter, that Stack Exchange uses, has been discontinued and is no longer being maintained. The repository has been marked read-only as well.
As such, no more languages will be added to the highlighter, and existing bugs with the highlighter will no longer be fixed.
Now that this highlighter is officially deprecated no longer maintained, can Stack Exchange please either switch to another highlighter that is being maintained, or begin maintaining their own highlighter (possibly a fork of Prettify)?
In my opinion, the best thing to do would be to begin maintaining the syntax highlighter internally. This way, bugs and feature requests with it can be filed and tracked on meta sites, and changes to it can be made more quickly. Under the old system, bugs with it would take a long time to be resolved (since it was only maintained by random people on occasion), and when they were resolved, it would take a lot of time for it for SE to eventually handle a feature request to deploy an updated version. The whole process would be drawn out and take 6-8 months-years. (As an matter of fact, I filed an issue with it back in 2014 and it still hasn't been resolved as of the discontinuation date.)
The best way to handle this would be to make an internal fork of Prettify, and start off with that.
I noticed some people would prefer using Highlight.js, which is actively maintained, but a prior request to change to that highlighter was declined for performance reasons.
This is not a duplicate of google-code-prettify seems dead since that was back in 2014 and the project simply languished (as opposed to being officially discontinued), and a few months after that question was posted, the project was back in action. However, that can't happen as the repository has been marked read-only, and probably won't happen anyway due to the official discontinuation.
To address animuson's comment:
I imagine that someone is simply going to fork this away and maintain it separately. To be clear: that hasn't been maintained by Google in many years. It was maintained by regular users who wanted to contribute to it and make it better. Nothing is stopping them from doing it somewhere else. [...] Some random Google employee archiving it doesn't break anything.
With the repository's archival, there is no longer a centralized effort to maintain the highlighter. It's quite possible that newer fixes might just end up in several independent forks that would have to be manually merged by SE.