Either I'd go with my "theory" above or hand-wave and say the aliens "did something" to Adams's character to think of time non-linerally and that it's not strictly an aspect of learning their language. Or perhaps, it's not necessarily something everyone can do, maybe she had a high enough IQ that she's in an elite 3% of human beings on the planet able to expand their mind enough in thinking in this language in order for it to have non-linear time effects. Everyone else would just learn the language enough to be able to communicate but not to think 4-dimensionally.
Because there was a bit of a "hiccup" in how that's explained. They say something like that when the aliens "write a sentence" (or equivalent to the circular formations they made" they had to know how the phrase ended in order to present it.
Which, er,.... Yeah?
Isn't that how sentences work?! I mean it may happen so quickly in our minds or subtly that you're not conscious of it but there's plenty of times when speaking you have to know what you're going to say before you actually say something.
In English, for example, take the articles a or an to know which one of these to use you have to know what the next word in the sentence is going to be and, somehow, we're able to do this instantly when speaking even if we've not fully thought out what we're going to say. You don't consciously think "Ok, I'm going to say a word that stars with a vowel-sound so I need to use "an." in British English it's the same thing when ending a word that ends with a vowel with an "R" sound if the next word is going to start with a vowel. So, simply speaking, even speaking English means you've got to be able to think a second or so into the future.
Other languages have examples like this to when they assign genders to nouns and the gender of that noun can have an impact on the articles or prepositions before it. Again, requiring someone speaking off the cuff to have to be able to think a moment into the future without realizing it.
Now, it's a stretch to say this but there must be "something" about the heptapod "language" that just gives them this much more of look into the future but, still, seems to me that'd require some "biological" component that makes these beings 4-dimensional ones, something beyond their language.
