I have solved it like this:
Interesting approach. Does this method allow use of only one culture specific property? I think I have to test it out.
It is possible, and I did it on one of the solutions I worked on a couple years back.
Grzegorz Wiecheć wrote how to do it 5 years ago https://gregwiechec.com/2015/07/localizable-media-assets/
If it is a plain new solution then it should be simple to add, but if the solution is allready up and running, you will get issues as the images that is allready uploaded doesn't have culture set in the DB, so that you need to set manual to your masterlanguage if I remember correctly. Unfortanly I don't think I kept the SQL script I wrote to fix it :/
But the old images should still be displayed, just will have issues editing/translating them
Since ImageData (https://world.episerver.com/csclasslibraries/cms/EPiServer.Core.ImageData) is not translatable we need to translate same descriptions and alternative texts over and over again in multiple locations, blocks, pages etc. where ever the image is used.
Issue is even more relevant now, that most governments require sites to be accessible.
There has been conversation about this missing feature over the years on Episerver World:
Would it be possible to re-design media types, so that those will also implement ILocalizable? Based on the response from support issue is following:
You can check the class structure of ImageData and there's a Blob properties. This means the object can perform streaming and file read/write and this obviously cannot implements ILocalizable.
Which means that probably media types should be wrapped to something to allow ILocalizable?