It's not only a Japanese thing. For example, English speakers use French pronunciation when referring to to "Grand Prix" racing events. We prefer to say "Gran Pree" or "Grom Pree" rather than "Grand Pricks" Sometimes "gran" indicates a phrase of Italian rather than a French origin. The GT badge on a sporty touring car refers to Gran Turismo, which Detroit mimicked (I think) with the "Gran Torino," ... although it might as well be "Gramp's Torino."