Add \t for tab and \n for new line.
\t
\n
Use \n for a line break and \t if you want to insert a tab.
You can also use some XML tags for basic formatting: <b> for bold text, <i> for italics, and <u> for underlined text
<b>
<i>
<u>
More info:
https://developer.android.com/guide/topics/resources/string-resource.html
\n didn't work for me. So I used <br/> HTML tag
<br/>
<string name="message_register_success"> Sign up is complete. <br/> Enjoy a new shopping life at fatherofapps.com!!</string>