https://archive.org/details/the-bhagavad-gita-s-radhakrishnanIf this is the primary source, use quotes from this book.
If Gita is written by many and in several languages, you should consistently use quotations from the version of the book selected as the primary source.
In this book, an English transcript is used to write Sanskrit - you can maintain this in using quotes for dissertation and if you want to , you can use another authentic Sanskrit version for the same quote in Sanskrit language.