This is a nasty bug for us, as we cannot fully translate our app. The bug is easily reproduceable on apex.oracle.com.
Create a classic report:
select empno, ename, sal, job from emp
Create an application translation and seed the translatable text.
The column headings are not available in the translation repository. Only this is available:
To make sure it is a CR bug, I changed the report to IR. Now the headings are available for translation:
