Impossible to add field to Form in Customer Portal when using JIRA in French

Steps to Reproduce:

1. Install JIRA 6.2.2;
2. Install JIRA Service Desk;
3. Create a Service Desk;
4. Modify the user's profile so the user will use French;
5. Click on 'Ajouter un champ' (Add a field) in the Customer Portal » Edit Form screen.

Actual Behavior

The add field screen is never displayed - in the Console of browser's Developer Tools "TypeError" is shown.