@gernot Only automatically managed strings can get their comment generated, and Xcode generates one as soon as it detects them in code and syncs them into the String Catalog.
The idea is that you are in full control over manual strings (the ones you add to the catalog yourself).
Because you already know how the new string is supposed to be used, you also know what comment is relevant for it.
In order to generate a comment, the string has to be used in code first. That means quite a bit of jumping back & forth to tell Xcode to generate a comment via the context menu.
But yes, please file a feedback if you think it would be beneficial to get a generated comment!