What language did the blackfoot tribe speak?

There were two different and unrelated tribal groups in North America referred to as "Blackfeet" or "Blackfoot" by white settlers.

The larger group lived (and still live) in Alberta, Saskatchewan and northern Montana. These were the Blackfoot confederation, made up of the closely-related Blood, Piegan and Blackfoot tribes. They all spoke an Algonquian language very distantly related to the languages spoken in the north-eastern States.

A much smaller group were the Blackfoot Sioux, a division of the Teton Lakotas of the Missouri river in South Dakota. They spoke the Lakota language and today they mainly live at Standing Rock Reservation in South Dakota.

Just to show the differences in their respective languages, here are a few Words in Algonquian Blackfoot and the equivalent in Blackfoot Lakota:

Algonquian Blackfoot .................... Blackfoot Lakota ................ English

ahkapi............................................ota.......................................many

ahmoki............................................sha......................................red

sik...................................................sapa....................................black

aapi.................................................ska......................................white

apsi.................................................wahin..................................arrow

omitaa.............................................shunka................................dog

ahkwiniman.....................................canonpa...............................pipe

stomick............................................p'ta.......................................buffalo bull

nahtoya...........................................wakan...................................sacred

ni't...................................................wanci....................................one

niisito...............................................zaptan..................................five

kiipo..................................................wikcemna.............................ten

kaiyo.................................................mahto..................................bear

ahki...................................................win......................................woman

aohkii.................................................mini.....................................water