If you understand French to a high level you will be able to follow the interesting ideas put forward in these essays. There are however plenty of English translations online which offer the same insight as the original.
The book is a dual language book in one sense with a modern french translation on one side and the original old french text on the other.
If you are buying this book for a University course then I would recommend owning this version as it is a fairly neat copy of the text.
If you are interested in the writings of Montaigne then I would also recommend it as an insightful read with a relevancy to modern day. I would, however, advise a very good level of French.