The textbooks published in the USSR had their copyright listed as "The Ministry of Education of the USSR." I am not interested in the "author rights." I am only interested in the copyright rights (a distinction that is probably more relevant to Germany than it is to the US anyway).
The UN view on successor states is that all states inheriting territory of a country become successor states unless (or until) such status is changed through bilateral agreements.
While the Russian Federation is considered a de facto successor state in most contexts, that's not good enough in legal contexts in which exact transfer of ownership needs to be established.
The link above states that Ukraine (by law) considers itself to be a successor state to the USSR. Which would suggest that it has not abandoned its right to inherit intellectual property owned by the USSR.
Is there is a clear case precedent on how this would play out in a US court? For example, let's say someone produces a derivative work (such as a translation) of an old Soviet textbook, but would only secure a permission to produce derivative works from the government of Ukraine. Would they be able to publish and distribute the translation commercially? Or would they also need to get a permission from the government of the Russian Federation?
Again, I am asking if there is precedent on this topic, not what the prevailing opinions are. Although, of course, if the legislation on the subject is clear and unambiguous, it would be useful to know that, too.