In like 224 of http://git.xfce.org/xfce/xfce4-power-manager/tree/src/xfpm-battery.c , it says "msg = g_strdup_printf (_("%s (%i%%)\n%s until is fully charged."), tmp, battery->priv->percentage, est_time_str);" it should be "until it's fully charged", not "is fully charged."
After cloning it from git, line 224 is currently: msg = g_strdup_printf (_("%s (%i%%)\nEstimated time left is %s."), tmp, battery->priv->percentage, est_time_str); which looks fine in my opinion.
Thank you for your bug report, this is a duplicate of bug #9322. *** This bug has been marked as a duplicate of bug 9322 ***