your dd is starting reception?
what exactly do you think they do?
it is like nursery, they do a lot of learning through play, learning vocab through play, exploring the world, developing motor skills, curiosity, looking at themselves and their families and differences with other families and ten mins a few times a day on the carpet with the white board, first of all learning phonic sounds and then later writing simple sentences.
The majority is independent or child led activities.
She wont be sitting anywhere wondering what is going on, she will be playing with sand water dressing up blocks, colouring, painting etc.
SOcialisation, kids dont even notice these differences you are talking about. they just see other children. the only way they notice is if you point them out. words are a small part of communication. body language, gesture, interaction in games, playing together in sand/water, copying each other, working together to build something, etc this is what children in reception do, nothing is stopping her having friends.
and the other children will very quickly learn English and realise English is for school and other language is at home.
the reason the Bengali kids didnt invite you back after school is because after school they usually go to mosque!
Like I said my kids are in mixed schools. my dd1 is in reception and never been invited to a friend from schools party or to their house, doesnt stop her playing with them at school and getting on with them etc. and she also has extra curricular activites where she socialises. I dont feel she is missing out, neither does she.