Taxonomy terms not translating on the edit/add node form
Best guess based on your description is that you need to enable the URL detection at


  /admin/config/regional/language/configure


since that appears to be how you are distinguishing the interface. This recipe from http://drupal.org/node/1281704#comment-5253460 should also help:


Enable ALL i18n modules
Add your extra languages
(optional) - Enable Localization update and run Update translations at /admin/config/regional/translate/update
Enable URL detection method at /admin/config/regional/language/configure
(optional) - Throw that Language Switcher block into a visible section of your site
Add your Localized vocabularies and translate them
Add your terms and translate them
Edit the content types you want term references to appear in and Enable Multilingual Support (with translation) in Publication Options vertical tab
(recommended) - In the Synchronize Translations vertical tab check the first two checkboxes of the Extended language options. That is: "Set current language as default for new content" and "Require language (Do not allow Language Neutral)"
Add term reference fields to the content types you want