Term translations across vocabularies

The current i18n interface does not allow to define term translations across vocabularies.

For example, given a vocabulary E whose language is English, and another F whose language is Français, if I want to translate terms of E into terms of F, the interface does not provide any way to create those translations.

Currently, the only way to translate terms is to place all of them in the same vocabulary, and to associate no language to that vocabulary... which leads to another issue: http://drupal.org/node/29697.