Every version of D&D published before 1989 explicitly included alignment language as a part of its rules, but this is one of the most mocked and maligned concepts in the game. In my opinion, it is unjustly disliked. I've said many times, I think alignment language works well as a communication medium in a three-point alignment system.
But I was looking through the AD&D Player's Handbook (first edition) recently and I thought a bit more about it. I like alignment language, and I really like the idea that Law / Neutrality / Chaos is how characters relate to a vast cosmic struggle. But I also like the idea of Chaotic Good characters who align themselves with Chaos as a force of ultimate liberation, or Lawful Evil characters who bend the seemingly benevolent aims of Law to enslave others. Some Neutrals seek a balance between the two great forces, for good or evil, while others are uninvolved in the fight.
So I think there is a compromise possible between the two, by using 9-point AD&D alignment but totally removing the moral axis (Good / Neutral / Evil) from both the cosmology and the alignment tongues. So as far as the vast cosmic forces are concerned, you are "Lawful" or "Chaotic" or neither. And characters who are Lawful go to Lawful Church and learn the Lawful language, while characters who are Chaotic are members of cults and learn the Chaotic dialect. The Neutral language may be an optional thing taught by druids and bards or philosophers and wizards.
One reason I'm really drawn to this is that it offers a model where religions have real corruption. A Lawful Church wouldn't be the same without corrupt prelates who are Lawful Evil and twist the religion's meaning, or even Lawful Neutrals who are so rigid they can't allow human decency into the equation. Chaotic sects likewise have members who are basically decent, and others who embrace the pure Chaos of their faith (Chaotic Neutral.)
An intriguing point is the existence of Lawful Evil or Neutral Evil monsters. LG PCs would be able to speak with LE opponents, and on a grand cosmic level be on the same "side," while on a human moral scale they are diametrically opposed.
(As an aside: I've been watching the History Channel Vikings show on DVR, and Floki is just such a terrific Chaotic Neutral character, without getting annoying.)
Moral alignment would impact on the system as well. For instance, Protection from Evil doesn't really make sense in a game where "Evil" isn't an alignment. Similarly, spells like Know Alignment would let you get one or the other aspects of a character's alignment; you can know that they are Evil, or that they're Chaotic, but not both at once.
I like the world that this implies. It's a bit darker, but still awash in alignment; people can ally on different grounds, the Lawful Good knowing that the Chaotic Good has totally different aims in the grand scheme of things but both working for the common weal, or the Lawful Good and Lawful Evil united on a big-picture issue while differing drastically in method and approach to fellow human beings.