Rudolf Fischer, who has died aged 92, was a historian, linguist and polymath who advised and guided foreign writers through the minutiae of eastern European history, language, etymology and ethnography; the foremost of these, Patrick Leigh Fermor, acknowledged in 1986 that his debt to Fischer was “beyond reckoning”.

First published in the Telegraph 12 June 2016.

Fischer’s friendship with Leigh Fermor began after Fischer wrote a letter to him full of praise for A Time of Gifts (1972), the first volume of Leigh Fermor’s travel trilogy, with, attached to it, a long list of all the inaccuracies, misspellings and contradictions. Months passed without a response, and Fischer feared that his constructive criticism had gone down badly. In fact, Leigh Fermor was delighted, and wrote, eventually, asking if Fischer could bear to advise on his next volume. Gradually drafts of Between the Woods and the Water starting appearing in parcels from the Peloponnese which Fischer pored over meticulously.

There resulted a correspondence which lasted for decades, thrashing out the finer points of Transylvanian history, language, costume, traditions and legends. Fischer also read and made corrections to Leigh Fermor’s final, posthumous, volume of the trilogy, The Broken Road, published in 2013, and edited by Artemis Cooper and Colin Thubron.

Among others he also helped Bruce Chatwin, Robert Kaplan (who devoted an entire chapter to him in Eastward to Tartary), Dervla Murphy, Colin Thubron, Robin Hanbury-Tennison, Adam Sisman and William Blacker, many of whom made the pilgrimage to his small book-lined flat in Budapest.

Rudolf Fischer was born on September 17 1923 in the medieval city of Brasov, Kronstadt, in the Transylvania region of Romania. His father, Josef Fischer, was a Hungarian Jew, a descendant of the Hatam Sofer, the 19th-century leader of the Haredic movement which resisted modernisation and mysticism. His mother, Bertha Meldt, was a Saxon Lutheran. Rudolf attended the local Saxon school. But talk of war prompted his father to migrate with him to Australia, leaving his wife and younger son behind, for fear that the older one, Rudolf, would be enlisted.

The next few years were spent helping his father on a chicken farm on the outskirts of Sydney and serving in the alien corps of the Australian army in New Guinea, before attending Sydney University, where he met his first wife, Janet Gleeson-White.

At university Fischer studied under John Anderson, a Scottish philosopher, whose acolytes formed the libertarian movement known as the Sydney Push, one of whose principles was that no statement or assumption was to remain unchallenged. This, as one writer on Australian philosophy, James Franklin, later observed, was all very well but “hard on the wives and children”.

In the early 1950s Fischer moved to Britain, earning a living as a teacher. He felt that cultural life of London compensated for the poor living conditions in an attic flat; it was a view not shared by his wife, who was struggling with small children. So in 1957 the family travelled back to Australia. The marriage broke down, however, and Fischer returned alone to Europe in 1962 where, on a visit to Romania, he met his second wife, Dagmar von Melchner, a distant cousin.

After living in Greece for eight months, the couple moved to London, where, in 1968, Fischer became English Language editor for the New Hungarian Quarterly – an achievement given that his first language was German – and so they moved to Budapest, where they remained for 48 years. There, with Dagmar, he brought up his second family, deepened his knowledge of Central Europe and became a guide, critic and friend to writers of all nationalities who passed through Budapest.

Fischer’s library was packed with obscure 19th-century reference books on the Balkans and the Austro-Hungarian Empire, as well as a large map from 1853 of Europäischen Turkei – more accurate, he assured everyone, than the modern ones. Rudolf Fischer was a link to the pre-war Saxon world of Transylvania, and with his fine moustache, upright and dignified manner, collection of exotic Eastern European hats and excellent grasp of all the relevant languages, he more than fitted the part.

He was buried in Brasov in the family grave in a small Saxon Lutheran cemetery at the end of the street on which he had been born.

He is survived by his second wife Dagmar and his five daughters.

Rudolf Fischer, born September 17 1923, died February 18 2016