Technically, a language delay means no Asperger's. It's in the current definition of the disorder.
There are several other language disorders that can look like autism but are actually something separate.
Under the DSM IV for Aspergers the no language delay is actually qualified in that it defines the lack of language delay to be that the child cannot put together 2 word sentences by age 3. This is actually at least a 12-18 month delay in skills. Thus a child CAN have a speech/language delay and still qualify for Aspergers so long as the child was able to make 2 word sentences by age 3.
We got a great explanation on this when they were doing rule outs on my son, who had a 18 month language delay, but was still looking at Aspergers, because he could make 2 word sentences.
YES several other disorders can look like aspergers and not be aspergers. My son's final dx were MERLD and CAPD. Combined with his ADHD-HI they did a great job of mimicing a lot of aspie type behaviors and tricking lots and lots of people into either ignoring or trying to write off the blatant signs that he wasn't on the spectrum.
Both MERLD and CAPD can have social awkwardness with them, but it stems from different sources. I will list some of my son's autistic "traits" and where we found they actual came from
1) echolalia - common sign of autism, his stemmed from his extremely poor short term auditory memory. He had to constantly repeat what he heard over and over two do two things, correctly process the information and store it in long term auditory memory. He will still parrot some today, but it usually only occurs when he's confused, frustrated/angry, the conversation is moving to fast for him (due to usually emotions) or he doesn't really understand what is being said so he spits it back.
2) lack of eye contact - another common trait of autism, but for my son, he lacked eye contact because he was attempting to read people's lips due to his inability to understand what they were saying and couldn't distinguish the voice from background noise.
3) sensory issues - another common thing found with autism, but my child's sensory issues stemmed from three things, his hyperactivity, anxiety, and ear infections (head/ear sensory issues). Currently, we only deal with the sensory needs stemming from anxiety (type A personality, perfectionist, in a not so perfect person)
4) social delays - another big autism thing, well if your already an anxious person AND you are only picking up 2 words out of every 10 said to you, and this leads to lots of mistakes, people looking at you funny, making fun of you etc.. well how social are you going to be? Further, add in that your an introvert and much more interested in things well above your actual age and its a recipe for social disaster. Also, the hyperactivity causes MANY adhd children to simply miss the minute physical and verbal social cues people give off because their minds (and bodies) are already 3 or 4 steps ahead of the current instance. I watch both my boys do or say something and then see the glimmer of realization of what they just said/did sink in a few seconds later as their brain processing what is going on catches up with what they are doing. Mind you both my boys have unbelievable high processing speeds as well, so a child with a normal processing speed, or many of the ADHD kids who have decreased processing speeds it will take even longer.
5) Another thing on social delays, my son gets easily embarrassed from messing up due to the anxiety and such and thus he is reluctant to put himself into a social situation or when he does, he gets SO excited that its happening that he becomes over aggressive regarding it (like not understanding why a child hasn't called when they said they would and that he should confront the child, which is what of course he's been taught to do with a problem, but its not appropriate for "this" social situation)
6) routines and rule bound - again COMMON autism signs, but they aren't singularly autism. My son is VERY rule bound, not because he can't break rules etc, but the anxiety of going outside them isn't something he can yet handle. He finds it very easy to break some rules, but not others (for example safety rules). He also MUST have advanced warning of a schedule change. If he doesn't know in advanced, he's likely to not hear/understand it when it just happens, thus does something wrong, and then the anxiety self doubt etc all kick in. Not something we deal with much anymore, but occasional it peeps back up. He used to need hours warnings, now he just needs to be told specifically right before it happens and perhaps giving a small explanation for why. It was never to the point that we HAD to do the routine/follow the rule without any change at all. Only that we had to prepare him for it. Today I can start out a trip saying we are going to x, then y, then z and after x say hmm I think we will go to Z then y and he's doesn't even blink. His obsessions are driven by anxiety, which is worsened, fueld by his hyperactivity.
I will add that with my son, when he gets emotional the first skills that go are his verbal skills. It used to be to the point that he couldn't articulate anything at all until he calmed down. Now, some of these things pop up, like the echolalia, saying nonsense, becoming rigid about the way things are to be done etc.. but these are all self protecting mechanisms that he has. Almost all his autism signs suddenly disappeared after about 12 months of treatment for his CAPD (and so did his MERLD). Now we are left dealing with residual stuff and strengthening his language/verbal skills (we now only have a 25-40 point gap between verbal and nonverbal skills, versus a 65-75 one)