Hi Andika,
Thanks for reporting this. Luckily it’s just a minor annoyance, COOL does not use gettext, we replace the literal ‘%0’ to a string by the code. But it does not have be ‘%0’. It could be ‘$0’ or ‘{0}’, whatever we like. So possibly, I’ll change this, not to annoy people who check their po files with msgfmt command. It’s not only about changing source strings, it requires changes in the surrounding code, too.