This paper reports on a study of the exciton polariton region in reflection spectra of wide CdTe/CdZnTe quantum wells (with well width exceeding by far the exciton Bohr radius) measured in Voigt geometry in a magnetic field. In a magnetic field, forbidden exciton lines were observed to appear for each exciton quantization level. The exciton diamagnetic shift constant has been observed to decrease noticeably with increasing number of the quantum confined level. A comparison of calculated with experimental spectra reveals a growth of the exciton translational mass with increasing magnetic field. It has been shown that both the growth of mass and the decrease of the diamagnetic shift can be traced to mixing of exciton internal with translational motion states.