Ours isn't an immersion Montessori school, but one of the main reasons I enrolled my children there is because it is fantastically multi cultural - There are guides from Japan, England, Iran, Iraq, Jordan, Turkey, Russia, Bosnia, America, and Italy. DD2's teacher is tri-lingual (speaks fluent Japanese and Spanish) and the other day I asked if she ever spoke to the children in different languages. She said no, but then asked if I wanted her to. I told her to feel free to speak Japanese and Spanish to my daughter! OF COURSE! And my partner is fluent in spanish, so they already know a bit.
They do have a spanish teacher (new this year) that will be a part of the program, but it's obviously not immersion.
I checked out a HeadStart classroom for DD1 last year and it would have been a total spanish immersion class for her. I just didn't feel comfortable with the security in the area the school was in.