'Gran Turismo' is for sure italian.
The french equivalent is 'Grand Tourisme', the english one 'Grand Touring'.
Racing competition makes a distinction between cars designed for racing (known as prototypes, racing cars...) and cars originally designed for a road use. The latter are called 'voitures de tourisme' in french ('touring cars' in english).
Among them, the top of the category are called 'voitures de grand tourisme' ('grand touring' in english, 'gran turismo' in italian)
Many championships involving road cars use this terms.
'Touring car' in :
- DTM (Deutsches Touringcar Meisterschaft)
- BTCC (British Touring Car Championship)
'Grand Touring' in :
- JGTC (Japanese Grand Touring Championship)
The terms GT has also been widely used for naming many sport cars (Opel GT, Porsche GT2...) and it has a positive meaning associated to sport and performance.
Pretty much like the 'A-spec' term in Japan.
Of course the game features cars from all 3 categories, but the term GT was chosen for the meaning I just mentionned.
(The longer this post gets, the less clear the explanation sounds to me, so I'll stop right now)
While Gran Tourismo is the equivalent Itlaian to the English Grand Touring, the meaning of the words (as opposed to litteral enterpration) is Big Drive. This is referring to the original GT races being Big Drives across country rather than Short Drives around a track. The original GT cars were simply race cars with simple fixed hard tops put in place to keep out bad weather, birds, and bugs.
A true GT car now is one that is optimized for long cross country driving at high (but not true racing) speeds. Creature comforts are much higher than in pure sports cars. Pure sports cars emphasized handling and acceration, had fewer comforts, were usually much lighter, and were more easily driven on tracks than GTs. The last Supra was a GT, the last RX-7 a pure sports car, get the picture?
Gran Turismo is Italian for the "Grand Tour", an actual race, by the way. It was originally a passage between adolescence and manhood long ago where a boy and his father travel in a two-seater car and go on a very long drive. Look in the GT2 manual for further information.