I found the same question on StackOverflowStackOverflow. Try this out:
One argument, in one place:
Mage::helper('module')->__('Hi %s, there is an error', $name);
Two arguments, in two places:
Mage::helper('module')->__('Hi %s, there is an error with code %s', $name, $code);
One argument, in two places:
Mage::helper('module')->__('Hi %1$s, there is an error. Your name is %1$s', $name);
Two arguments, swapping places:
// Template or block file
Mage::helper('module')->__('Hi %1$s %2$s, there is an error', $firstname, $lastname);
// CSV translation
"Hi %1$s %2$s, there is an error", "%2$s, %1$s received an error"