Pending Approval Email can be translated by the user in the defines language file. E.g. put _UE_MYAPPROVALMAIL in the field in CB config, and a define for that in the language file. That's mentioned in the doc.

Idea here is that as it's a user-provided field in the main config, the use will want to personalize the text anyway.

But it's right that it would be nice to be able to translate its default text.

The proposed code change would work, but would start translating new way old defines which are not in defines file. That's something that was scheduled for CB 2.0.