The .in.in file was added to the repo in 8bdfa6a4e56f. Then Gary added the .in file to POTFILES.in in 1d98555... but I think it should actually be the .in.in file, right?
#!/bin/sh
METHOD_NAME=$1
iftest-z"$METHOD_NAME"
then
cat<<EOF
This program calls purple API functions using DBus and prints the return value.
If you are not interested in the return value, use purple-send-async.