Are historical claims restricted by the language they use?

Language is the human capacity for acquiring and using complex systems of communication, and a language is any specific example of such a system. Languages evolve and diversify over time, and the history of their evolution can be reconstructed by comparing modern languages to determine which traits their ancestral languages must have had in order for the later developmental stages to occur. Academic consensus holds that between 50% and 90% of languages spoken at the beginning of the twenty-first century will probably have become extinct by the year 2100, I find this statistic quite astonishing! This puts several historical and pieces of work in to question, as yes they can be interpreted and analysed however the analysis and interpretations of them are analysed through the eyes of people with the knowledge of a 21st century person, thus the meaning of historical claims are not quite spot on and not in any way what one would call reliable due to a change in meaning of certain phases and thus, our understanding of history and the distant past is most definitely unreliable and flawed.