In these cases the child becomes a "cultural mediator". He/she can only sustain this function as long as his/her cultural background is respected. Otherwise the "acting as a translator" will be accompagnied by a loss of esteem for his culture of origin.

I agree with Evert Jan. You have to be aware of the role
you give to the student by asking for an interpretation.
I would not draw the line between more or less official
communication between school and parents and informal
assistance within a class setting. Both are just examples.
The distenction has to be based on possible temptations
for misuse of power. We have to be aware of the situations
we create for our students. We can expect them to help us,
but we also have to know how that influences the social
structure.

I think you should distinguish between the use of a minority language in peer interaction during classroom activities and the official communication between the school and the parents from immigrant families. I see no harm in involving pupils in translating and explaining learning tasks to fellow students in whatever language they want if the environment is receptive to plurilingual and intercultural education and as long as it is not seen as an "ultimate solution" . Definitely harmful is "using" the students for formal communication between the school and the parents. Schools should be prepaired to communicate in other languages as well, especially towards communities with many newcomers. Why not involving bilingual parents in cultural mediation and translation tasks?