To get this achievement, you must put the word, "ALPHAJAX" on the board in an online game. This does NOT work on a 'local user' game.
You can do this with a secondary account. Just make sure any letters your secondary account has gets exchanged into the bag.
You can use one or two blanks, and the achievement will still pop.
It may help to remind you that the only two letters words involving the letter X are AX, EX, OX, and XI, and XU.