What is the black foot translation of word sister?

There is no language called "Black Foot". It's likely you're referring to the Blackfoot language, also known as Siksika, spoken by the Blackfoot people of North America.

In Blackfoot, the word for "sister" is "akikii" (pronounced "ah-kee-kee").

However, the exact word may vary slightly depending on the specific dialect of Blackfoot and the context.