Is the Kolmogorov k^(-5/3) law for the energie spectrum E(k) in freely decaying turbulence a realy universal law ? I am interested specialy in stratified turbulence, does the law above exist in this case , or does any other laws exist ? can anyone tell me about this subject ?

Yes, Kolmogorov k^(-5/3) also exists in stratified turbulence. (Ref: Stull R B, an intruduction to Boundary layer Meteo.(1988)). However, it seems to me stratified turbulence is a very hard topic, intermittence, week turbulence, non-equilibrium etc.

Sometimes minor intermittency corrections are added to the K^(-5/3) law. If the stratification effects are very high (e.g. across thin exothermic flames), then the K^(-5/3) law may not hold. If the stratification effects are small compared to the inertial effects, K^(-5/3) usually is a good approximation even without any intermittency correction.

Sreenivasan (Physics of fluids, 1995) has done a nice job of gathering data on lots of different types of flows and presenting the spectral scaling for them. Take a look at this paper to see if you can find better answers to your question.