Continuing the discussion from Translate sidebar documentation links:
Similar to the above-mentioned feature request, there is currently no translation of custom sidebar content. This is true both when the custom sidebar section is created and deemed globally-visible by an admin, and when created by a user for personal use.
Translation may not be necessary in the latter case, since the user would likely create the sidebar section in their own language, but when an Admin adds a custom sidebar for all to see, ideally, each user will see it in their own language.
(Edited to add: I originally wrote this post as a separate feature request topic, but @Moin pointed out it was a duplicate, so I’ve merged the two.)