Actually the string 'synchronize drawing to the vertical blank' in compositor in xfwm4 isnot available for translating

so why this string isn't available for translating?
I have in spanish xfwm4 at 100% time ago before 4.11 but that string isnot in the list.

PD: additionally I do tweaks to the already 100% for many components, please update the already 100% .po files too, maybe some others do the same, but arn't updated again fi they reach 100% even if a big change is done.