Have you tried using a standard lng variable like {$lng.txt_welcome}, or a similar language variable you're familiar with, in its place? If it printed that would most likely prove whether the var you have created is at fault or not (I would have thought).
Can you search for your language variable directly by inputting the variable name in the filter under languages?
For example, in admin, this page below should give a result... (although you may have some different requirements to be entered below)
Code:
languages.php?language=US&topic=&filter=txt_delnote
Does it contain a value? Is it simple text (no HTML included)?
I know the questions are silly to ask - but you never know.