This page explains the current status of the translations in GnuCash. There is a separate introduction into Translation in general, but this page explains where you are invited to work on and where not.
See also http://lists.gnucash.org/pipermail/gnucash-devel/2009-January/024700.html but the branch names there are not any longer up to date.
Unstable 2.5.x releases
As of May 2013, we are releasing 2.5.x versions regularly and they should now include the correct translation as well. Releases are planned for the first week of each month until we're satisfied with the quality, at which point we will release 2.6.0, with a current target of last week of December 2013. String Freeze is active as of November 2013 (release 2.5.7) in order to provide translators 2 months, including a release, before the stable release.
The 2.5.x release series ("trunk" branch) is now the current place where translation work should be done. All translations from the 2.4 branch have been copied over to trunk on 2013-05-07 (and subsequently merged with trunk's pot template).
Again: Please work on the "trunk" branch of SVN for your translation work, if you retrieve the code from SVN.
No more gnucash-2.4.x (probably)
The development of the 2.4.x branch has ended in spring 2013! Gnucash-2.4.13 was (most probably) the last release of that branch. Please do not continue any translation work on the 2.4 branch of GnuCash!
No more gnucash-2.2.x
The development of the 2.2.x branch has ended in spring 2009! Gnucash-2.2.9 was the last release of that branch. Please do not continue any translation work on the 2.2 branch of GnuCash!
No more gnucash-2.0.x
The development of the 2.0.x branch has ended in spring 2007! Gnucash-2.0.5 was the last release of that branch. Please do not continue any translation work on the 2.0.x branch of GnuCash!
No more gnucash-1.8.x
The development of the 1.8.x branch has ended in fall 2005! gnucash-1.8.12 was the last release of that branch. Please do not continue any translation work on the 1.8.x branch of GnuCash!