standard letters, German has three vowels with Umlaut, namely ä, ö, and ü, as well as the Eszett or scharfes S (sharp s) which is written "ß". German orthography has gone through a series of reforms, the most recent in 1996. German dialects are distinguished from varieties of standard German. German dialects are traditional local varieties and can be traced back to the different German tribes. Many of them are not easily understandable to a speaker of standard German, since they often differ in lexicon, phonology, and syntax. Around the world, German has approximately 100 million native speakers and also about 80 million non-native speakers. German is the main language of about 90 million people (18%) in the EU. 67% of German citizens claim to be able to communicate in at least one foreign language, 27% in at least two languages other than their first. In the German diaspora, aspects of German culture are passed on to younger generations through naming customs and through the use of spoken and written German. The Goethe Institute seeks to spread the knowledge of German culture worldwide. A total of 15.5 million people are currently learning German as a second language. Literature German literature can be traced back to the Middle Ages, with the most notable authors of the period being Walther von der Vogelweide and Wolfram von Eschenbach. The Nibelungenlied, whose author remains unknown, is also an important work of the epoch, as is the Thidrekssaga. The fairy tales collections collected and published by Jacob and Wilhelm Grimm in the 19th century became famous throughout the world. Theologian Luther, who translated the Bible into German, is widely credited for having set the basis for the modern "High German" language. Among the most admired German philosophers and authors are Lessing, Goethe, Schiller, Kleist, Hoffmann, Brecht, Heine and Schmidt. Nine Germans have won the Nobel Prize in literature: Theodor Mommsen, Paul von Heyse, Gerhart Hauptmann, Thomas Mann, Nelly Sachs, Hermann Hesse, Heinrich Böll, Günter Grass, and Herta Müller. Philosophy The rise of the modern natural sciences and the related decline of religion raised a series of questions, which recur throughout German philosophy, concerning the relationships between knowledge and faith, reason and emotion, and scientific, ethical, and artistic ways of seeing the world. German philosophers have helped shape western philosophy from as early as the Middle Ages (Albertus Magnus). Later, Leibniz (17th century) and most importantly