Like said, the translation started before the localization announcement.
It is only a menu patch, and the team stopped when Nintendo announced the European localization.
The tools are available for people wanting to still try it before the launch (I was curious how the game looked like), or for translating in other languages not included in the future official release.
There's no rules saying that a team have to stop translating when a language is available.
It's like some games which are re-translated by fans, even though they are already in english. It's just a project like another, by a team who like doing it, whatever the reason. I think hackers learn a lot from any project, useful or not for the end user.