How to add translated images

[m-kuhn]

Todo, work out where translated images have to be placed.

[sjib]

https://help.transifex.com/en/articles/6240942-localizing-images

[ponceta]

Every translatable image should be renamed like my_great_screenshot_en.png where translators can change _en to _fr, _de, _it, ...

Every generic image (suitable for any language) does not need this _en filename extension.