or contribute to open source
Multisites are notoriously difficult to find supported plugins for, for the simple fact that not many people use them and they are a difficult thing to get right. The annoying issue for multisites is that they lack a single media library. You can do dumb stuff like duplicating media for each subsite, but that is more hassle than worth thinking about.
When we took on our first internationalisation project, I was quietly confident that there would at least be some third-party plugin that would work if I couldn’t manage to figure out how to do it myself.
Whilst there are certainly options on Envato that claim to do what you want at a price, I started to get a little worried when realising they are very few and far between. So, I prayed to the open-source gods of Git to provide me with an answer. And they did, sort of…
There is a Git repository by some guys called Human Made, and their plugin is called Network Media Library:
It is a few years old (2019) and there appear to be subsequent projects they’ve worked on. However, I could not get those to work for love or money so I’m assuming they aren’t compatible with the latest version of WordPress or I’m doing something dumb.
But what I could get to work (sort of) was this 1.5 version of the plugin, although it’s ACF functionality didn’t work the way I needed it to. So you need to either: comment it out or adapt to whatever works for you. As long as you get the media ID to show, you’re golden. What is very reassuring is that the plugin itself is one file, it’s tiny! You’ll need to add some minor tweaks like pointing out which site library you want to use etc, but you will eventually get it to do everything you need.
The unexpected benefit I discovered is that because we’re using the media ID for the reference, rather than the URL, when the image is called into the page, it is localised to that sub-site folder eg website.com/en-gb/media.jpg etc. So whatever language site we export it to the onpage media URLs will all correspond to the correct sub-site.