FWIW, I worked with the children of migrant Mexican families in farming in the US from 1993-1999. My specialty was education of children with special needs and disabilities.
We dealt with one family who had a daughter with significant delays, mainly b/c where they had been in Mexico, her "condition" was considered to be an embarrassment for the family, and they hid her in the home and from visitors, and the siblings were told not to mention that she existed. The mom had worked in a chemical factory in Mexico while pregnant, and this child was born with many challenges. The child had never been to school and never really even out in public when we (literally) found her hidden in their apt.
Her family loved her very much, but culturally, they had been so accustomed to keeping her away from society b/c they were ashamed, that they had no idea that there were services and schooling for children with special needs in the US. The mom was so grateful when we found her and told her that we could help. She obviously loved her daughter very much, but since the mom had no education at all, either, it was a HUGE challenge.
The little girl regularly attended school (most migrant kids miss a ton of school, but she was always there). We had a zillion specialists working with her, but since she was about 12 and never had any kind of formal language, not Spanish, not English, not sign language, but a few "home signs," it was INCREDIBLY difficult to make much progress.
Developmentally, if people do not "get" a formal language by age 8, it is highly unlikely that they will ever be ABLE to acquire formal language. Those neural transmissions just don't develop after that age. (This is one of the reasons that many Deaf advocates encourage use of ASL when children are young, even if the family insists on English down the road, so that the critical language development years are not "lost," but that is a separate, heated argument.)
HTH.