History books have a reputation of being dry and from my point of view reading a work from 1960 compared to a work from 2012 the difference in the language is minimal except for a few different words being used. So the questions i ask are:
Is the language of history books prone to changes in popular language?
How much has the language changed from the first acknowledged and sourced history book to books of the late 2000s?
Is the language of histroy books prone to changes in popular language?
Yes. Absolutely. History writers are just as prone to linguistic change as any other author or segment of the population. Not only does the vocabulary and style of writing change, the manner in which a certain historical topic is approached has changed drastically as well. It is a bit difficult to notice a change between the 1960's and now because written English hasn't changed that drastically in the past 50 years.
The easiest way to demonstrate this is to take a look at a much older piece of historical work such as Friedrich Schiller's History of the Thirty Years War in Germany and just compare the style of writing with more modern pieces of history. Not only is the writing style 'old fashion' but the narrative itself is much more traditionally grounded i.e. it shows direct cause and effect relationship while many modern histories would bring up the controversies and possible other effects causes of each event (if that make sense).
The manner in which History is studied and written has changed radically in the past century. In Germany, the field of Alltagsgechichte or 'Everyday History' has pushed many historians to study the day-to-day life of average people or people generally 'ignored' by history such as farmers, factory workers, women and children. In France the works of Foucault have had a global impact on the study of history as his work concerning power and control over knowledge has become commonplace in historical discourse.
Your question revolves around Historiography or the methodology used by historians and also the development of the field of history itself (The history of history in other words.) There might be a good overaching text about Historiography that someone else could recommend but it is a pretty big topic to cover.
Long story short, the way history is written has changed drastically and your question is very general that it is difficult for me to answer it sufficiently. If you could maybe narrow down your area of interest it would help as different fields of history have been affected differently by various philosophical movements at different points in time.