Hi.
I've translated the Gallery Pro latest 3.0 version to Spanish. I attach the traslated file. The file is for utf8 users. If you use a ISO standard language just rename the file to "Gallery.spanish_es.php". However note that some strings should be changed. Edit the file and replace as follow:
á = á
é = é
í = í
ó = ó
ú = ú
For capitals are: Á and so on.
ñ = ñ
After that, just upload the file to:
directory where SMF is installed/Themes/default/languages/
Cheers!!
Edit.
I edited the file for ISO users and is also attached.