You don't overwrite the gravityforms.pot file, you have to use a PO editor to generate a language specific file. That file will then have a filename of something like this (German example):
You then have to generate the MO file from this which would have a filename like:
Please note the example above is using German, hence the de_DE in the file extension. The .mo file would then go in the languages folder. In order to activate it you would have to setup your WordPress site to use whatever language it is.
You can't localize just the plugin, your entire WordPress install has to be localized and setup for the language you want to use.
Here is a tutorial on how to translate a WordPress plugin:
Posted 13 years ago on Sunday September 12, 2010 | Permalink