Is there an IC which converts I2C/UART/SPI (or any standard communication interface) commands directly to DALI2 format?
Microchip have some parts that support DALI such as PIC18F26K83 using a modified UART peripheral. You still need the high voltage and polarity insensitive interface circuit externally but this could simplify your design.
Whether this is suitable depends on your application. I believe it can be used for control gear (slave) and for single master with receive capabilities, but if you need multi-mastering as defined in IEC62386-101 then check with them - the data sheet isn't clear how it copes with timing windows defined in the standard.