Fix custom languages not retrieving trans

[pablotransifex]

Problem and/or solution

Problem: when user declares in zendesk non standard locales, their respective translations are not beign fetched from TX Solution: get the zendesk locales from api/v2/locales.json instead of getting them from api/v2/locales/public.json

How to test

Reviewer checklist

Code:

• [ ] Change is covered by unit-tests
• [ ] Code is well documented, well styled and is following best practices
• [ ] Performance issues have been taken under consideration
• [ ] Errors and other edge-cases are handled properly

PR:

• [ ] Problem and/or solution are well-explained
• [ ] Commits have been squashed so that each one has a clear purpose
• [ ] Commits have a proper commit