I recently answered a question on the Joomla forum that had a quick and easy answer.
Question was: "I just want to customized the 'Thank you for your e-mail' message you get after sending an email with joomla form.?
Fortunately, this question had a very easy answer:
The text of this message is part of the Joomla language file, and you can easily change it.
To edit the language file, go to Site -> Language Manager -> Site Languages.
Click on <English> (or whatever language you are using). This will load the language file into your editor.
Scroll down until you see the following line:
Simply change those words to whatever you want. So, for example:
Watch your quotes / single quotes carefully.
Once you have changed the message, simply save the file and the next time, that message will be displayed.
Extending the Answer
There are a lot of Joomla's standard messages that can be customized here.
If there is a page with no articles on it, Joomla says "There are no items to display." You can simply remove that message be editing it out in the language file.
There are a lot of messages in Joomla that can be easily customized by editing the Language File. Take a look around there. You might find something you'd like to customize. But, watch those single quote marks!