This guidance relates to Cite Them Right Harvard style.
The 1978 ebook is available to University of Worcester staff and students. It contains Vygotsky's earlier works translated and published into a book, and those papers were written prior to his death in 1934 - not in 1978. The book was translated and published by Cole and others with their own additional material.
The reference for this book can be tricky and some people have given the question a lot of thought! There is no 100% correct answer on this one - the main thing is to make sure the reference for the source you have read is traceable by the reader.
In Harvard style, one suggestion for an in-text citation might be Vygotsky (1978). You may want to acknowledge the context of Vygotsky's work and when it was published in your writing, for example:
In a 1978 translation of his work, originally written in the 1930s, Vygotsky (1978) explained that....
A suggested reference for your reference list:
Vygotsky, L.S. (1978) Mind in society: the development of higher psychological processes. London: Harvard University Press.
