It seems that after Roberto Romero abandoned the maintenance of the Wesnoth Spanish Translation team in 2007, it’s all gone downhill.
(Fun fact: it was under his leadership that I contributed my first translations for mainline Wesnoth — my first involvement with a FOSS project ever.)
Some time after he left the team (apparently without previous notice to Ivanovic or Torangan), the translation was taken over by a significantly less competent group that did a very lousy job (read: no quality control) before abandoning it again. Around the end of 2008, I took it over and quickly, with the help of an Argentinian guy who joined me later, brought it to completion in time for the first release of the 1.6 series.
In the process I realized how hard it really is to maintain a complete translation of a large game like Wesnoth.
Due to a series of RL complications, I had to abandon the Spanish translation shortly after Wesnoth 1.6 was released (March 2009). The translation was not taken over by anyone in time for Wesnoth 1.8 (April 2010). Much later in November, though, a new fellow became maintainer and got some work done along with other new collaborators.
Things were starting to look unusually bright because, for the first time in years there was more than one active translator. However, this world full of rainbows and pink unicorns did not last, and it ultimately fell into oblivion following the departure of this last maintainer from the community. No-one took over the team afterwards, and now the Spanish translation is in its natural state once again. The last update in mainline trunk took place in January 2011.
You can have a look at the current situation in gettext.wesnoth.org, our translations statistics website.
It seems that Battle for Wesnoth just doesn’t manage to appeal to many Spanish-speaking people from the FOSS users community to attract new individuals with the knowledge, patience and time required to resurrect an abandoned translation, and the sense of leadership required to coordinate work and keep certain quality standards to attract and, most importantly, keep new translators.
Of course, Wesnoth is a huge undertaking of its own with over one dozen of thousands of strings in mainline and its distinctive approach to storytelling — I know for sure I do not want to work on translating campaigns again, at least, not alone. Still, there are people far more capable than I am for this kind of work, and I do believe our game could really use more publicity among Spanish and Latinamerican players and their contacts.
All the technical fluff relevant for starting to work on an existing or new translation can be found in the wiki, after all.