If you need two variables in the XML, you can use:
%1$d text... %2$d or %1$s text... %2$s for string variables.
Example :
<string name="notyet">Website %1$s isn\'t yet available, I\'m working on it, please wait %2$s more days</string>
String site = "site.tld";
String days = "11";
//Toast example
String notyet = getString(R.string.notyet, site, days);
Toast.makeText(getApplicationContext(), notyet, Toast.LENGTH_LONG).show();