Converting raw temperature data to Celcius L3GD20
You're confusing the operating specifications of the chip with the readout format.

Basically, the Electrical characteristics specify the range of temperatures at which the IC is guaranteed to work properly. This is a physical characteristic of the device. As the datasheet says Operating temperature range, e.g. this is the temperature range over which the IC is supposed to work properly. It has no relation to the theoretical range of the register containing the measurement value.

The temperature sensor readout is specified as "-1 °C/digit". Therefore, each increment of the temperature output equals one degree C. My guess would be that the value of the temperature readout would probably directly correspond to the actual IC die temperature in degrees C, though you should verify this.

The two specifications are unrelated. It's like a car speedometer. My car's speedometer goes up to ~150 miles/hour. However, it's not intended to actually be driven at those speeds. As such, the readout range (0-150 Mph) significantly exceeds the intended operating conditions (~0 - ~85 Mph), as they're different characteristics.