> copyright governs copies, it doesn't govern ideas or algorithms

The second part is true. The first is a little trickier. The copyright applies to some fixed media (text in this case) rather than the idea expressed, but the protections extend well beyond copies. For example, in fiction, the narrative arc and "arrangement" is also protected, as are adaptations and translations.

If you were to try and write The Catcher in the Rye in Italian completely from memory (however well you remember it) I believe that would be protected by copyright even if not a single sentence were copied verbatim.