As an Autistic person myself, and as a person knowing many autistic people, I can assure you we indeed are capable of language. Even very low functioning autistic individuals are at least somewhat capable of speech, this is not true in all cases, of course; but it is not, in the majority of cases, to the degree of them being incapable of language comprehension or acquisition.
Here are some examples, and also, the reason you cannot find scientific papers on it is because there is no reason whatsoever to make a peer reviewed paper on the topic of Autistic people being able to understand language, as we all already know that to be the case, and already know why it is the case.
That being, Autism is a Spectrum Disorder and can have various different intensities, and even than, like all Mental Disorders, it does not always manifest in the exact same manner. For example, look at the manner used for diagnoses in the DSM-V, (https://asatonline.org/for-parents/diagnosis/)
Criterion A: social communication deficits, consisting of three items, all of which must be met to satisfy this criterion;
Criterion B: fixated interests and repetitive behaviours consisting of four items, of which at least two must be met to satisfy this criterion;
Criterion C: symptoms existing in early childhood;
Criterion D: symptoms impairing functioning; and
Criterion E impairments are not better explained by intellectual disability (intellectual developmental disorder) or global developmental delay (APA, 2011; CDC, 2014).
All five must be met, but they are all very wide in nature, and none of the criteria include impairment in general language comprehension ability, and, as the anecdotal evidence supports, one very much can have Autism and have high language ability
American Psychiatric Association [APA] (2011). DSM-5 https://www.dsm5.org
Centers for Disease Control [CDC] (2014). Diagnostic Criteria for 299.00 Autism Spectrum Disorder https://www.cdc.gov/ncbddd/autism/hcp-dsm.html.