Don't use \n sequence inside Lisp strings needing translation...

... Because xgettext will just remove the \, not replace \n with newline.

That's consistent with Lisp reader behavior in this documentation:
http://www.lispworks.com/documentation/lw70/CLHS/Body/02_de.htm

The XLisp reader, which replaces \n with newline, is nonstandard.

So, to accommodate xgettext, use (format nil "...~%...") instead, or where
you can't do that in a $ header line, just make a line break inside the ""

There are a few "\n" left alone in sample-data-export.ny which are neither
in $ lines nor inside (_ "...")

plug-ins/vocoder.ny

@@ -136,4 +136,4 @@ $control radar-f (_"Frequency of Radar Needles (Hz)") real "" 30 1 100
           (0 s)             ; let Audacity coerce back to stereo
           (1 (vector original s)))))
  (t                         ; this effect isn't meant for mono
-  (_"Error.\nStereo track required.")))
+  (format nil (_"Error.~%Stereo track required."))))