When the ambient temperature is between 30 to 35 °C in summer, will lettuce seeds germinate?
Lettuce seeds show "high-temperature inhibition", or, plainly put, won't germinate at temperatures over 85 °F / 30 °C. Considering the fact that they are native to the Mediterranean, that's a wise mechanism: summers tend to be dry there and the seeds would be at risk of drying quickly.
While they will germinate between 40 and 85 °F / 5 and 30 °C, you will get the best results in the 55-70 °F / 12-21 °C range.
If your nights are cool, sowing in the evening and shading / watering during the day might suffice; otherwise consider germinating them indoors, e.g. using the paper towel method or flats / trays, then transplanting them. Don't forget to harden them off, in this case not because of the temperature, but because of the sun, and choose heat-tolerant breeds or your lettuce will bolt and get bitter quickly.