Inserting a carriage return into t()
Never had a usecase for that and no working Drupal 6 installation, but I assume your problem isn't t() related, more PHP related.

&lt;?php

// This does not work!
echo '\n';

// This does work on UNIX!
echo "\n";

// This does work on Win!
echo "\r\n";


Hope this answers your question and helps.