There seem to be a couple of different questions and concerns in this post that have been confused (the first step: clarify the question). One seems to be the q

There seem to be a couple of different questions and concerns in this post that have been confused (the first step: clarify the question). One seems to be the question of why we study old philosophers in the first place (1), another is the question why we study them in their original language (2). The most discernible answer the author proposes, to the first question at least, is that reading old philosophers is a way of learning about the methodologies employed by a philosopher. My brief response... (2) The original text is the original data. The first task is to understand what exactly it is that a philosopher said. Nailing that down can itself be the subject of debate. As multilingual people who've used more than one language in the course of intellectual work know, translation is often an approximation of the original text. Language is bound up with culture and what words denote, their connotations, their significance, etc, aren't always translatable in a straightforward fashion. By comprehending the language, we have a better grasp of the content the philosopher was trying to communicate to us. That doesn't mean good translations can't exist, but that, too, can be the subject of debate. From there, we have all manner of commentary which begins a tradition and can spin off into still other traditions. Science operates in essentially the same way. There is a scientific tradition with important figures that have initiated fruitful traditions themselves and who are likewise inheritors of still older traditions. Some traditions fade for a number of reasons. Understanding both the commentary and the original text can clarify things better than understanding just one of the two. Your understanding becomes more perfect. (1) The notion that philosophical theories at time T+1 are necessarily better than those at time T is an appeal to novelty, i.e., a fallacy. Theories fall out of favor not necessarily because whatever takes their place, so to speak, is more formidable. That kind of progress isn't a given nor is it that straightforward. For example, that Cartesianism and its fallout has dominated a good chunk of western thought for the last few centuries does not mean that the Aristotelianism it "replaced" was inferior. In response to the proposal that we read Aristotle to absorb his methodology, I'd like to answer in the context of what I wrote above. The methodologies he uses are communicated through the tradition and numerous commentaries have been written on the methodologies Aristotle employes (they vary depending on the subject matter he is attending to). However, it is a mistake to think that that is the only thing Aristotle offers. Aristotle's methodology, after all, is a means to the truth. Philosophy is a theoretical endeavor where "theoretical" means it is done to know things for their own sake.