CAPD stands for Central Auditory Processing Disorder. Here's the definition according to adoption.com:

Central Auditory Processing Disorder (CAPD): This term describes a condition in which the affected individual, whose hearing capabilities are otherwise functionally sound, will have difficulty understanding and processing information that is heard. It is believed that this occurs as the result of a communication breakdown somewhere between the ear and the parts of the brain that receive and interpret hearing stimuli. All of the possible causes of this disorder are still not known, but those that are known include: head trauma, lead poisoning, and possibly chronic ear infections. Because of the wide variety of possible causes of this disorder, and the strong likelihood of the existence of multiple contributing causes, each suspected case needs to be carefully evaluated on an individual basis.

Now, why would this be a special issue of children adopted from Russia? Head trauma and chronic ear infections are probably equal-opportunity issues for adopted or non-adopted children, and while lead poisoning is an issue in children adopted from Russian orphanages, according to one study summarized here, only about 5% of children adopted from Russia showed elevated lead levels.

The answer to this question has to do with institutionalization, lack of stimulation to the brain and the nervous system, and first language/second language learning difficulties. This article, from Family Focus, the FRUA newsletter, explains that typical ESL learning patterns do not apply to children adopted from institutions, because these children are not typical:

It is also known that young children learning a second language use a variety of cognitive and social strategies to help them learn the new language. We need to keep in mind, however, that most internationally adopted children are not typical children. Because of the trauma and neglect they have experienced, they may not have the capacity or resources to use the strategies that more typical children employ. Also, as noted above, institutionalized children frequently are delayed in their first language, which can affect their second language development.

Here's a great article on CAPD and children adopted from institutions from the National Coalition on Auditory Processing Disorders. In it, the author explains why, in institutions, children may not have received the auditory stimulation needed to create proper auditory functioning:

Children who have been institutionalized may have undergone auditory deprivation. How can they learn to distinguish one voice from another when the sounds of their world, in the orphanage, are a jumble of many children and infants crying or, perhaps, music played randomly without purpose other than to, hopefully, soothe the children. For many, the music can serve as auditory stimulation, but stimulating what processes? This can lead to underdeveloped or malformed processing capabilities in many.

CAPD often goes along with SPD (Sensory Processing Disorder, or Sensory Integration Dysfunction) and other alphabet syndromes. An audiologist gives the evaluation for CAPD. Many times, children's auditory processing problems can improve immensely with therapy.

Here's a great story from Rainbowkids about a girl who was adopted from China with CAPD, her diagnosis and treatment. I think it paints a very hopeful picture for people whose children might have this problem.