Than you Edu, in my case it works well.
I generated:
sudo locale-gen es_AR.UTF-8
Generating locales...
es_AR.UTF-8... done
Generation complete.

Here is the explanation (from Fran's blog, thanks!)

1. Check the name of the needed locale:

$ grep es_ES /usr/share/i18n/SUPPORTED
es_ES.UTF-8 UTF-8
es_ES ISO-8859-1
es_ES@euro ISO-8859-15

We want utf8 support, so…

2. Generate choosen locale:

$ sudo locale-gen es_ES.UTF-8
Generating locales...
es_ES.UTF-8... done
Generation complete.

3. Check it?

$ locale -a
C
en_US.utf8
es_ES
es_ES.utf8
POSIX

I was needing to add a locale tu my Ubuntu....here I found it.