Immediately, in reading this question, I am drawn to seperate the two themes: Multicultural voices and grammar. In order to do the question justice I will tackle each part seperately and then settle on a middle-ground.
In order to include multicultural voices in our classrooms we first need to create/establish an environment where children/students feel comfortable and safe. Especially in the US, where it has been drawn to my attention that racism and homophobia are still VERY apparent! i.e. Many citizens are unwilling to accept (or even try to accept) such 'touchy' topics, and when they do they can be/are hostile and aggressive.
Multicultural voices, to me, covers every 'difference' in every peron/community/culture that that sets us appart from one another, it what makes us unique and should be celebrated NOT condoned. In respects to the question I would suggest, once children know they are safe and feel comfortable, they shoud be given the opportunity to explore/vocalise their cultural voice...whether it be their native language/mother-tongue, talk about their religious beliefs, about their home country/where they originated from, their sexual orientation, their passions and hopes for their future etc...whatever thier cultural voice is it should be explored!
I believe identity is something to be cherished and protected, everyone should be proud of thier identity and what it means to them as a person. Most of us are very quick to defend our identity and we understand that it should not be questioned...some people don't have that luxury...take for example the Native Americans (Indian tribes) who have been opressed and abused, and have not been able to celebrate their culture and ancestry in the public eye. In the classroom we need to take control as educational leaders and set an example of being respectful of differences in any way, shape or form.
As for Grammar, we have been looking at Ebonics in 'Language in the classroom', and how it is been/is viewed by the predominantly white middle-class education system. In the past Ebonics was viewed as a language for 'idiots'...a language that did not pay attention to 'proper' spelling, punctuation and grammer...a language of the 'black african american people'. In my opinion Ebonics (eg. wha'tcha doin' back there missy?) is an expressive language stemming from and modifiying typical English American language. Aslong as children are taught the culturally accepted grammatical rules so they can apply this academically to develop in their literacy learning etc...I believe expressions/differences in grammar from county-to-country, culture-to-culture can be explored and acknowledged in positive environment.