Is there a good way to test this?

Yes, run the command in the README like:

python3 ./build_docs.py --quick --build-root ./build_root --www-root ./www --log-directory ./logs --group $(id -g) --skip-cache-invalidation

you can limit it to one language and one version for a faster build by adding --language en --branch main.

Ah, I almost opened a pull request for this, you were quicker :D

I ran:

python3 ./build_docs.py --quick --build-root ./build_root --www-root ./www --log-directory ./logs --group $(id -g) --skip-cache-invalidation --language en --branch origin/main

I didn't get any console errors, but also didn't see the switchers:

I then did two languages and two versions:

python3 ./build_docs.py --quick --build-root ./build_root --www-root ./www --log-directory ./logs --group $(id -g) --skip-cache-invalidation --language en fr --branch 3.13 --branch 3.12

And served the pages via python -m http.server -d www, but again saw no switchers for any of the four.

In my version, I can't see the switchers until I resize the page enough to see the mobile view. It works as intended and no JS errors. Is this the case you're facing too @hugovk?

Ah right, thanks, and I had old results in the www directory so this time I deleted it first.

rm -rf www
python3 ./build_docs.py --quick --build-root ./build_root --www-root ./www --log-directory ./logs --group $(id -g) --skip-cache-invalidation --language en fr --branch 3.13
python3 -m http.server -d www

Here's main on the left, with console errors and no switchers; and this PR on the right with no errors and switchers:

<select> is missing in the switcher div, switchers.js is not populating it for some reason:

How it should be:

Okay, looks like it's working now at the top:

And in the mobile sidebar:

There was a problem that $('.version_switcher_placeholder') returned all placeholders, but document.querySelector('.version_switcher_placeholder'); returned only the first. So we need to use querySelectorAll and loop.

There was also a possible issue with adding too many quotes near the quote_attr calls.

I'm very happy to see this land, thanks for the work!