Problem in update po

Hi. I'm new here and i have some question.
I read the docu about localization and i followed the step in it. And the language pack is already have so i just have to update it. I used the poedit to edit the .po file but nothing changed when i refreshed my web page. And then i tried to copy the .mo file that appear when i modify the .po file to the locale folder (e.g I modify the .po file in the po folder of themes matrix folder and copy the .mo file to the specify language folder in locale folder of matrix folder). But there was nothing happen when i refreshed webpage. Would somebody please tell me why isn't it change? And some advice how to fix.
Thank you very much.