You correctly note that the main limiting factor for this sort of thought is the scarcity of canon material.

It has been hypothesized before that certain differences in pronunciation between Alduin, Paarthurnax, Odahviing and Durnehviir are dialectal. However, it quickly becomes frighteningly messy to distinguish voice actor slip-ups from real rules, and as for lexical variation, there is simply too little content to base any solid conjecture on.

Interestingly, all canon dragontongue displays some properties of slang. For instance, the zero copula (zu'u hin daan "I'm your doom") seems to occur more frequently in emotional speech. Word Walls often omit entire particles (praan nu denek Keizaal "rests now in the soil of Skyrim"), which hints at a Nordic form with even simpler grammar than usual.

There are two other types of contractions to note. The first is losei "you're," a contraction of los hi that appears in a single line: Ful, losei Dovahkiin? "So you're the Dragonborn?" As the dictionary notes it can only be used in questions, since los hi means "are you."

A more important contraction is the -a/-ha suffix that indicates to-infinitive verbs ("to kill," "to fly," etc.). Curiously this can be used to contract both "{verb} wah" (Rok funta koraav "He failed to see") and "wah {verb} (Boaan tiid vokriiha suleyksejun kruziik? "Has the time come to restore the ancient dominion?"). The latter isn't really a contraction in the strictest sense, but something to be aware of.