Yup, you can create your own localization file.
1. Create a localized YOUR_WPLANG.mo file from languages/testimonials-widget.pot. See [Translation Tools](http://codex.wordpress.org/Translating_WordPress#Translation_Tools) of [Translating WordPress](http://codex.wordpress.org/Translating_WordPress) for help.
2. Create a directory named languages inside of wp-includes.
3. Put your YOUR_WPLANG.mo file into your wp-includes/languages directory.
4. Set WPLANG inside of wp-config.php to your chosen language. See [Using Localizations](http://codex.wordpress.org/Translating_WordPress#Using_Localizations) of [Translating WordPress](http://codex.wordpress.org/Translating_WordPress) for help.
5. The default WPLANG is en_US. Use en_US.mo as the filename of your localization changes if you’re sticking with US English.
Good luck!
