Banshee has been translated into dozens of languages, but if the translation for your language doesn’t exist or is out of date, you can help bring Banshee to entire new populations simply by translating some text.
You can see how thoroughly (if at all) Banshee is translated into your language. Then, you can read about translating GNOME applications, and if applicable, contact the existing translators or translation team for your language to coordinate.
To translate Banshee, you can download the po files, or download the development version of Banshee.