approach charts
 

Are the instruments approach charts calculated in standard atmosphere ?
(case of the actual altitudes in ISA minus ...)

Yes,

that's why you have different TL stated when qnh drops below a specific value..;and for NPA (non precision approach) where no electronic path exist to Xcheck your actual altitude, you have to consider corrections according to the deviation from standard..

So in all case you'd better know how the non standard conditions could affect altimeter readings...

rgds