how to test .po translation file? Portugeuse help?

I have made my plugin with language support (I hope!) and created a .po file . Someone has used the po file to create a portuguese translation.

how to do I test it out, I tried changing the wp_lang bit in the config file to PT but the plugin was still using english, I checked with another plugin that has language files (xml sitemap) and it was also in english but the rest of the standard dashboard options were in portuguese

would any kind Portugal soul care to download and test the plugin to see if it works with the Portuguese translation file?
Commentluv plugin