Order of I2C signals on the header
I am wondering are there any standards for the order of signals on I2C header? [...] I understand that I2C is typically used within the board itself and hence order may not be defined.


The order of pins on any I2C connector is not defined in the I2C specification. Therefore any connector used for I2C, and the order of signals on that connector, are chosen for other reasons.

The I2C specification does recommend a PCB or ribbon cable "wiring pattern" as follows - this does not specify pin order on a connector, but is relevant:



(Image source: I2C specification section 7.5 - Wiring pattern of the bus lines)

Some companies have made their own standard connector pinout for I2C e.g. Seeed / Seeedstudio Grove I2C devices. However any connector / pinout standardisation cannot be relied upon for other products, which don't claim to meet that company-specific "standard".

These previous questions also discuss I2C signal order on connectors:


Is there any definitive I2C pin-out guidance out there? Not looking for a &quot;STANDARD&quot;
At what point does crosstalk on I2C become a problem?
Crosstalk through I2C