We have studied the localization of two-dimensional exciton states in II-VI heterostructures by compositional fluctuations of solid solution, forming the quantum well. It is shown that due to the two-dimensional character of exciton motion in quantum wells, the effect of compositional fluctuation on exciton states is much stronger than in three-dimensional solutions of the same composition. The method for calculation of the density of fluctuation states below the edge of two-dimensional exciton band and the spectral density of exciton transitions is developed. The classification of states with respect to its migration properties and contribution to the luminescence processes has been carried out using the continuum percolation theory. As a result, the shape of emission band, its relative shift with respect to absorption band and the position of mobility edge are calculated. The results of calculations are in good agreement with the experimental PL and PLE spectra of ZnSe superlattices with submonolayer insertions of CdSe.