Is there a minimal legal ground clearance to use an international airport?
For propellers, there is a minimum ground clearance according to the EASA Easy Access Rules for Normal, Utility, Aerobatic and Commuter Category Aeroplanes (CS-23):


  CS 23.925 Propeller clearance
  
  Propeller clearances with the aeroplane at the most adverse combination of weight and centre of
  gravity and with the propeller in the most adverse pitch position, may not be less than the following:
  
  (a) Ground clearance. There must be a clearance of at least 18 cm (7 in) (for each aeroplane with
  nose wheel landing gear) or 23 cm (9 in) (for each aeroplane with tail wheel landing gear)
  between each propeller and the ground with the landing gear statically deflected and in the
  level, normal take-off, or taxying attitude, whichever is the most critical. In addition, for each
  aeroplane with conventional landing gear struts using fluid or mechanical means for absorbing
  landing shocks, there must be positive clearance between the propeller and the ground in the
  level take-off attitude with the critical tyre completely deflated and the corresponding landing
  gear strut bottomed. Positive clearance for aeroplanes using leaf spring struts is shown with a
  deflection corresponding to 1.5g.
  
  (b) Aft mounted propellers. In addition to the clearance specified in sub-paragraph (a) an aeroplane
  with an aft mounted propeller must be designed such that the propeller will not contact the
  runway surface when the aeroplane is in the maximum pitch attitude attainable during normal
  take-off and landings.


So 18cm seems to be the minimum ground clearance for propellers on most aircraft (e.g. ATR-42).

It is hard to prove a negative, but the section about turbojets and turbofan engines does not list any minimum.