How media translations work primarily depends on how they have been created and edited in the Mission Center.
Addition in the training course default language
By default, media are shared between the default language and the translations of the training course activities. When an image or video is added in the default language (let's take English for example here), the same media is automatically used in the various translations.
If you change this same media in the default language, then the change will be reflected and the same media will be modified in all translations.
Customizing media in a translation
If you want to customize a media in a translation (for example, for an image with embedded text), you must import the image into the translation (the card where the image is located) (French for example), which will "dissociate" the image in the French version from the on in English. But the default language image will be kept for other translations (Spanish for example), unless you change it in those translations as well.
At that time, if the English image is changed (default language), it will replace it in English and Spanish but the French image will remain the same, since it has already been replaced on its side.