The above post is basically perfect. Yeah, these are consequences of writing half this system in a caffeine-fueled haze of sleep deprivation.
So, first, a question - what is your opinion of a more elegant solution? Everything has a personal truename, or drop personal truename rules for unintelligent objects and locations?
Successful saves don't affect the range, but a failed check does (the latter causes you to actually speak the shortened utterance, you just wind up using a longer action for it). This is what I intended, at any rate, and I'll go clarify that a failed check makes you actually speak the shortened utterance, and a successful save changes the effect on a subject (but only on that subject).
I'll clarify that I meant that it's impossible to tell the difference from an epistemology perspective. That was a really vague statement of mine. You would know the effect of a particular utterance affecting you if its speaker so desired, but not anything else about it, such as what utterance it actually was (unless you could make the truespeech check).
Law of Sequence - When you fail a Truespeech check, you actually speak the shorter utterance. So if you fail to speak the sentence of fire, you actually speak the word of fire. If one of the creatures targeted made its saving throw, it (but not necessarily the others) would be affected as if by the syllable of fire instead (which would then interact with other utterances as the syllable of fire, since that's what is affecting the target).
The Law of Immiscibility was an old name for the Law of Uncertainty. Thought I'd cleared those up, thanks for pointing it out.
It should be a swift action. I'll clarify that, since it'd still be necessary for intelligent magic items.
One question - in writing this, I've been assuming a distinction between the act of taking an action, and the effects that action generates (the distinction between the act of spellcasting and a fireball). Is that a distinction the rules actually make in a sensible way? The rules for shortened utterances are intended to rely heavily on this distinction.
EDIT: After making the changes mentioned above, I'll be taking a short break. Once I get back, I'll get the lexica I have done posted (only one for each dialect, unfortunately), plus a few bits of miscellaneous material (feats, variant True Dragons, because Skyrim, and a masterwork tool). I can say right now that the Truenamer class is bland, and needs work.
MOAR EDIT: Should the Law of Resistance apply to all utterances from the same lexicon, or only identical utterances? I went with the conservative option, but I want to see what the opinions are. It might be necessary to see actual lexica before making that call, though.