Poedit application is the popular application uses to edit po file translation and it’s free. Click here to download Poedit application.
Now download and install Poedit application. Open language file you want to translate for example en_US.po You will find all English string in Source Text box.
Select text string you want to translate, add your translation text to “Translation” field. Once you finish translating. Save the file and it will automatically compiled to .mo file.