I don’t know which sidebar are you speaking about. If you meant the left sidebar, its links are as useful as on any other page, and is collapsed into dropdown menus on small screens anyway. The padding I’m speaking about is whitespace with literally nothing in it (it’s about 1-2em on each side, but I think 0.5em would be far enough).

In Vector on Special:Translate there is a way to collapse the sidebar manually or automatically on smaller screens.

Timeless adapts itself pretty well except that the middle column is narrower. That is probably on purpose, but doesn't work that well on the more complex UIs of Translate (Special:ManageTranslatorSandbox and Special:SearchTranslations also have issues).

Maybe the Timeless developers have ideas what can be done here.

Does the change in T165945: Timeless: Re-evaluate width cutoffs resolve this issue?

No. That change is to modify the width thresholds for the different layouts. My problem is that there is too much padding in the narrowest (mobile) layout.

Might be useful, as it should implement a specific single-sidebar setting: T131803: Options to only use a specific layout/not go bigger - single-column with only dropdown menus, or one sidebar-only

Though if a user sets theirs to single-column mode I dunno if trying to reuse that for single-sidebar would then override it. I don't know, I'll maybe figure it out later...

Can someone confirm if this is still an issue, and where the problematic paddings are presenting themselves at this point? (Is it added by translate, only on particular resolution layouts, etc?)

It looks resolved to me. @Tacsipacsi can you confirm?