It seems that when doing translations for Youtube videos, the only place where I can actually see the list of what I've translated is by going to Profile -> Activity, and extracting data there. Why external videos aren't simply included in the My videos tab?
Thank you for this interesting question, Błażej Porwoł.
True, the Activity subpage tends to be very crowded as it includes all subtitle revisions created by a given member. So it is indeed a bit awkward to find one's work there. However, having a separate page for the videos you add to Amara is also administratively needed.
So, to simplify finding your work, you could bookmark the subtitle sets you've made / collaborated in. A bit DIY, granted, but in my experience, it works.