Translation Macro fails to retrieve macro descriptor

STEPS TO REPRODUCE

1. Edit a page in CKEditor mode
2. Click on "XWiki Macro" Button
3. Search for Translation Macro and click 'Select'
4. Fill in the required fields
5. Click 'Submit' and 'Save&View'

EXPECTED RESULTS

The Translation Macro is working properly.

ACTUAL RESULTS

When selecting the macro (Step 3), an error is displayed on the 'Edit Macro' box which prevents the 'Content', 'Key', 'Locale' and 'Parameters' to be displayed:

Failed to retrieve the translation/xwiki/2.1 macro descriptor.

The issue could not be reproduced on CKEditor Integration 1.29.