"Normal" language. Language is one of 3 domains of impairment for a child to qualify for a diagnosis of autism. Delayed language is an exclusion for asperger's disorder, but normal language (not counting problems with articulation (clarity of speech)) not just in terms of understanding and using words but also in using language to communicate with others age-appropriately would make autism most unlikely.
Socialcommunication. Toddlers with autism can acquire words without using them to communicate. What's important is joint attention(toddler and parent interested in the same thing), reciprocal social communication to share interest (mommy, plane!) and, later, answering "w" questions (what do you do when you're hungry?) non-verbal communication is important (pointing at item of interest, then looking at you).