@Coding Badly:
That is a very good hint to save a lot of work, thanks a lot for that.
I thought having a SDA and SCL for a chip is sufficient to work with the libs.
So, why does these libs do not work with the ATtiny4313 ? The docs show that the ATtiny85 and the ATtiny4313 do have a SDA and a SLC and TWI (I2C) is supported.
Sorry for my questions but I am not a hardware specialist.