The Content Translation contributions pop-up location and behavior assumes that it's a link at the top of the screen, and it's broken in the Timeless skin.
In Timeless, most of the personal menu is hidden by default and appears on hover as a pop-up vertical menu, so reaching the Contributions pop-up is hard.
For now this is not an urgent bug to fix in Content Translation because Timeless is an optional experiment. However, it's worth thinking how can this pop up be made more robust and adapt itself to different skins without making assumptions about the location of the Contributions link.
Related task: T177143.