The local structure of molten CsF-AF (A = Li, Na, K and Rb) has been studied by high temperature Nuclear Magnetic Resonance (NMR) spectroscopy. The 19F and 133Cs chemical shifts have been measured as a function of the molar fraction of CsF. 19F chemical shift varies linearly with composition while 133Cs chemical shift presents a break around the eutectics composition. Furthermore, in molten CsF-LiF at high CsF concentration, 133Cs chemical shift is nearly constant. The evolutions of 19F and 133Cs chemical shifts versus CsF-AF composition have been interpreted as a signature of dynamical local scale distribution heterogeneities.