_cupsLangPrintf do not output anything

[bui]

I compiled cups 1.3.9 for my mini40 ARM board. when I type cups command such as lpc, lpinfo, etc, I see nothing on the screen. For example:
#lpc
?
help


quit
#lpinfo -l -v
#

I edit the lpc.c file by replacing the _cupsLangPrintf macro by printf. For example

replace _cupsLangPrintf(stdout,_("lpc>")) by printf("testlpc>")

Now I can see "testlpc>" on screen when running lpc
#lpc
testlpc>
testlpc>exit
#

My question is why _cupsLangPrintf doesn't print the output to screen? What dependencies it needs?
What is the file in which _cupsLangPrintf is defined? Can i replace it with printf and will it affect the operation of CUPS?

Thank you very much