Spoiler Alert: Not much!
I estimate that 97% of citations in the most prestigious English-language philosophy journals are to works originally written in English. In other words, the entire history of philosophy not written in English (Plato, Confucius, Ibn Rushd, Descartes, Wang Yangming, Kant, Frege, Wittgenstein, Foucault, etc., on into the 21st century) is referenced in only 3% of the citations in leading Anglophone philosophy journals.
Let me walk you through the process by which I came to these numbers, then give you some breakdowns.
I examined the latest available issue of twelve highly regarded Anglophone philosophy journals (the top 12 from Brian Leiter's 2013 poll results). [Note 1] From each issue, I analyzed only the main research articles in that issue (not reviews, discussion notes, comments, symposia, etc.). This generated a target list of 93 articles -- hopefully enough to constitute a fair representation of citation practices.
I then downloaded the reference section of each of those 93 articles, or for articles with footnotes instead of a reference section, I hand-coded the footnotes. I included only actual references to specific works. For example, the word "Kantian" would not qualify as a reference to Kant unless a specific work of Kant's is cited. For each cited work I noted its original publication year and original publication language. [Note 2]
This generated a list of 3566 total citations to examine.
Of the 3566 citations included in my analysis, only 90 (3%) were citations of works not originally written in English. Sixty-eight of the 93 analyzed articles (73%) cited no works that had not originally been written in English. Eleven (12%) cited exactly one non-English work, either in its original language or in English translation. Fourteen (15%) cited at least two works originally published in a language other than English. The only source languages other than English were ancient Greek, Latin, German, French, and Italian. No African, Arabic, Chinese, Indian, or Spanish-language works were cited in this sample.
Sometime after World War Two, English became the common language of most scholarship intended for an international audience, even when the writer's native language is not English. English-language articles citing only recent sources might therefore be expected to cite almost exclusively English-language sources. With this idea in mind, I divided the data into four time periods: ancient through 1849, 1850-1945, 1946-1999, and 2000-present.
Obviously, there's a huge skew toward more recent work -- but even in the 1850-1945 category two-thirds of the citations in this sample are to works originally written in English.
In my own writing, I also cite mostly English-language works. It's the tradition I operate in, and although I have some reading practice in French, Spanish, German, and classical Chinese, untranslated works are always a struggle. I don't intend to be too judgmental or blaming. But it does seem likely that the Anglophone philosophical tradition would benefit from more engagement with works not originally written in English.
Note 1: The journals were: Philosophical Review, Journal of Philosophy, Nous, Mind, Philosophy & Phenomenological Research, Ethics, Philosophical Studies, Australasian Journal of Philosophy, Philosopher's Imprint, Analysis, Philosophical Quarterly, and Philosophy & Public Affairs. This list has surface plausibility as a list of the best-regarded journals in mainstream Anglophone philosophy. Philosophers Imprint publishes rarely and sporadically, so I just used all of 2016 up to Sep 7.
Note 2: In some cases only the date of a recent edition was listed. In these cases I estimated publication year based on my knowledge of the history of philosophy. In some cases, only the English-language title was given -- and again I estimated the original language based on my knowledge of the history of philosophy. It is possible that I misclassified a few works in this way. However, for the estimate to rise to 3.5%, I would have to have misclassified 35 non-English works as English, which I believe is unlikely. (By the way, for these purposes, Web of Science is full of relevant mistakes. This more labor-intensive approach yields much cleaner results.)
The Ghettoization of Nietzsche (Aug 23, 2012)