If Contact Rating of switch is 5A 240V AC & 0.25A 240 DC, Then is this switch can be used for contact rating of 220V (+10, -15% voltage variation) AC & 127V (+10, -15% voltage variation)
The contact rating is the voltage/current that the switch can repeatedly connect and interrupt without degrading it's design life-cycle operation count.
Take the ratings as the maximum safe operational ratings of a switch. Yes, a 240VAC 5A rated switch will operate just fine on 127 VAC, but up to 5 Amps.
The DC rating is almost always lower because of the ability of switch to quench the arc when opening a DC circuit.
The max current that won't over-heat the contacts; the max voltage that won't burn them by arcing during break.