I have an I2C adapter for my LCD display i used with my Arduino.
Both are 5V logic, and i know that the pi GPIO are 3.3 V.
If i only need to "write" to the LCD, do i absolutely need a Logic level converter ?
You can't just write to an I2C bus. The SCL line is an output from the master (Pi) but the SDA line is an input and an output.
The LCD should not have pull-ups to 5V on board but many do. Perhaps connect it to 5V and ground and then measure the voltage on the LCD's SDA pin. If it's 5V you definitely should use a level converter.
As Joan has answered it depends on the pullups. The Pi has 1.8kΩ pullups on board.
I would just remove any pullup on the module, and it will work.
NO you cannot use a resistive divider.
SDA is bi-directional, so needs level converters.
SCL is output, so no need, but I would be unhappy connecting any 5V without a converter.