//file: cart.en.php
//...
echo '<title>Shopping cart</title>';
//...
echo 'Copying file ' . $strFile1 . ' to ' . $strFile2;
//...

//file: cart.de.php
//...
echo '<title>Einkaufswagen</title>';
//...
echo 'Kopiere Datei ' . $strFile1 . ' nach ' . $strFile2;
//...

//file: translationl.en.inc
$arTranslation = array(
 'title' => 'Shopping cart',
 'copy_1' => 'Copying file ',
 'copy_2' => ' to '
);

//file: translationl.de.inc
$arTranslation = array(
 'title' => 'Einkaufswagen',
 'copy_1' => 'Kopiere Datei ',
 'copy_2' => ' nach '
);

//file: cart.php
include_once( 'translation.en.inc');
//...
echo '<title>' . $arTranslation['title'] . '</title>';
//...
echo $arTranslation['copy_1'] . $strFile1 . $arTranslation['copy_2'] . $strFile2;
//...

//file: cart.php
//...
echo '<title>' . _('Shopping cart') . '</title>';
//...
echo sprintf( _('Copying file %s to %s'), $strFile1, $strFile2);
//...