Comment 10 for bug 1464855

baltasarq, thanks to your comment I found the problem. I started with other locale, Esperanto and zoom worked. So I investigated further and found an illegal character in the Spanish translation.

A quick and dirty fix (I'm on Debian, but it should work for Ubuntu too):

$ sudo bash
# msgunfmt /usr/share/locale/es/LC_MESSAGES/pinta.mo | sed 's/{0}.%/{0} %/g' | msgfmt -o /tmp/pinta.mo - && mv /tmp/pinta.mo /usr/share/locale/es/LC_MESSAGES/pinta.mo
# exit
$

You might have to do a "sudo apt-get install gettext" before.

What this does is: it uncompiles the Spanish translation, removes the offending character, compiles the translation again and then moves it to the right location.

I also made a pull request to fix it in the source code: https://github.com/PintaProject/Pinta/pull/128