There is great difficulty in translating sign language for deaf people with moderate intellectual disabilities. I believe that there are other methods that facilitate sign language communication with them.
In my opinion, a simplified sign language with signs used in Key Word Signing can be used for deaf people with moderate intellectual disabilities. Key Word Signing is manual signing for only the words that carry the most important information instead of signing for each and every word. Along with Key Word Signing, Gestures, Facial Expressions can be used to strengthen the message and to enhance receptive and expressive communication.
Other AAC methods like Communication Boards and Books, AAC Speech Generating devices can also be used to improve communication in deaf people with moderate intellectual disabilities.
Modified sign language should be used. The signer should focus on passing important information only rather than being to verbose (sic). Additional communication modalities such as picture board should also be employed to assist in passing the message and also developing a conversation.