Therapists often tell families to only speak English so as to not confuse the autistic child. I think that's not a good idea as it results in a loss of cultural identity. During my elementary years there was so much time spent on teaching me St Patrick's day (what relevance do green men and rainbows have for me) instead of say teaching me about Diwali (more relevant to me). Many of us have extended family who only speak their native tongue. Life exists outside of the special education classroom and therapy.
Autism loves to get stuck on sameness, so you may be inadvertently encouraging that very thing. For instance, in my early years - I used to watch Thomas the Tank engine pretty obsessively. I would avoid the Ringo Starr narrated version but loved the George Carlin version - the Brit accent felt like an alien foreign language.
It's good to also be exposed to different accents associated with the different languages for another important reason. We will be be surrounded by caregivers/educators with diff accents. No one thinks about this aspect.
I had a class aide in elementary who's accent I never understood. She was a new immigrant who was barely learning to speak English herself and I just could not make out her high pitched accent. It was not due to cognition on my part, how could I respond if I have not understood the question/instruction which as far as I was concerned was in an alien language. Sometimes I would try to watch her lips, trying to synchronize the visual of her lip movements with the audio I was hearing - it was a lot to process and it was often easiest to give up and engage in stimming behaviors (comforting) instead. Rather ironical as she was supposed to be teaching me. No one thinks about this aspect.
Anyway, I did get over the Ringo Starr thing eventually. Interestingly, the accent thing is not so striking in singing. I love Beatles music (simple lyrics that you can actually get your mouth around) and i did not realize Adele was Brit till i saw her talk at an awards ceremony.
