This topic added the original chinese Larudino package to PlatformIO: How can i add a boards that can work with arduinoide
For the lgt8fx core you pretty much do the same: Create your own framework-arduino-avr-lgt8fx packges which is correctly formatted (package.json, see mine), define your board files with the right core, variant and bascically all other settings that your target core defines in its boards.txt (you seem to have already done that). Then select the board via board = wavgatnano in the platformio.ini and see if it compiles.