For each language you can create unique content with completely different images.
You can do it using Media Gallery (it exist for articles, products, collections and pages content block).
To insert image into collection description, follow next steps:
- Open necessary collection.
- At the content editor menu find "Insert Image" button.
- In the opened media uploader select exist image or upload new with "Upload" button at the bottom.
- Press "Insert Image" button.
- Click primary "Save" button.