You can use String Overrides modules for overriding any string that passed through t().
Here are some details about this module from its project page:
Provides a quick and easy way to replace any text on the site.
Features:
- Easily replace anything that's passed through t()
- Locale support, allowing you to override strings in any language
- Ability to import/export *.po files, for easy migration from the Locale module
- Note that this is not a replacement to Locale as having thousands of overrides can cause more pain then benefit. Use this only if you need a few easy text changes.