How to Translate?

Hi,

I wanted to make a translation of the plugin, but so far i am yet to successully make the translation being used by the plugin.
I am editing the .po file with Poedit. I tried to change the name in severeal ways:

agm_google_maps-pt_PT.po
pt_PT.po

I am translating it to portuguese (Portugal). Many times, it's just a matter of getting the name right. Can anybody help me with this?

(yep, the language of the wordpress instalation is set to pt_PT in the options and the wp-config file)