UPDATE :
These seem to be the first Buddhist texts ever translated into English, published in 1693: THE LIFE OF THEVETAT , Translated from the Balie (i.e. Pāli)
An Explication of the Patimouc, or Text of the Vinac More information can be found in A philological approach to Buddhism by K. R. Norman, p. 4: Simon de La Loubère [...]
in 1687-88 went to Siam as an envoy ofthe king of France (King Louis), and on his return wrote a book about theKingdom of Siam, which was published in France in 1691.
Two years later anEnglish translation was published in England.
La Loubère gave a fascinatingaccount of many aspects of Siam and Siamese culture, and he also included anaccount of the Siamese religion — Buddhism — and the sacred language of theSiamese.
He noted the differences between that language, which he called Balie,and the Siamese language, and noted, correctly, the relationship between theformer and Sanskrit.
He also gave French translations of a few Buddhist texts.
Here is the English edition of Loubère's whole book, which contains the above-mentioned texts: A new historical relation of the kingdom of Siam by Monsieur De La Loubere ...
; done out of French, by A.P. Gen. R.S.S. London: Printed by F.L for Tho.
Horne ...
Francis Saunders ... and Tho.
Bennet ..., 1693.
Some other translations that can be regarded as quite early, include: The History and Doctrine of Budhism :
Popularly Illustrated: with Notices of the Kappooism, Or Demon Worship, and of the Bali, Or Planetary Incantations, of Ceylon by Edward Upham (London, 1829): contains translations of some Jātakas The Catechism of the Shamans (London, 1831) by Charles Fried.
Neumann :
contains translation of portions of a Mahāyāna Vinaya from Chinese Fragment of the Lotus Sutra translated from French by Elizabeth Peabody in 1844
(Wikipedia incorrectly calls that the first English translation of a Buddhist text) None of these publications seem to have made a big impact.
In 1844 the magazine published Peabody's translation of a portion of the Lotus Sutra from French [...].
The publication ceased shortly thereafter in April 1844.
buddhism.stackexchange.com/users/760/michau
As to the first notable translation, I would give this honorary title to Max Muller's translation of Dhammappada , first published in 1869 , later included in Muller's Sacred Books of the East series published around 1880s .
Beside Dhammapada, the series included important suttas such as Setting the Wheel of Dhamma in Motion, Mahaparinibbana, and others, all of Sutta-Nipata, most of Vinaya, one of the earliest post-canonical texts Milinda-panha, a Chinese version of the Life of Buddha by Asvaghosa, and some of the most important Mahayana texts such as Heart Sutra and Lotus Sutra.
Arguably this was the most notable early publication of Buddhist texts into English.
buddhism.stackexchange.com/users/43/Andrei Volkov
It depends somewhat on what you mean by a Buddhist text.
The book of “Barlaam and Josephat” is a famous Christian reworking of the life of the Buddha.
It was translated from Latin to Middle English in the 15th century.
buddhism.stackexchange.com/users/380/fdb
Sándor Csoma de Kőrös (Hungarian: Kőrösi Csoma Sándor) was a Hungarian-Szekler orientalist who went to Asia around 1820 looking for the ancestors of Hungarians, but ended up in Tibet instead.
He is well known among Hungarians for his journey and for compiling the first Tibetan-English dictionary and grammar .
He spent considerable time in Tibet studying Tibetan and Buddhist philosophy between 1827-30.
He was declared Boddhisatva in 1933 in Japan.
While I do not know if he translated Buddhist texts into English, it is plausible that he may have, as he immersed himself in Buddhism.
Unfortunately it is unlikely that this will be easy to research on the internet, you may need to go to dusty old libraries to get definitive information
;-)
Nevertheless, I thought that this was a good lead which is worth mentioning (since the dates are similar but a bit earlier than in the other answers).
buddhism.stackexchange.com/users/808/Csomakőrös
Some of the earliest translations are covered in the Sacred Books of the East ( Dhammapada by Max Müller based on a Latin translation by Viggo Fausböll and Sutta-Nipata by Viggo Fausböll ) series by Max Müller in which some of the books are Buddhist books as per the Theravada tradition .
More notable translation work (in the Theravada tradition ) has been done by Thomas William Rhys Davids who founded the Pali Text Society .
buddhism.stackexchange.com/users/295/Suminda Sirinath S. Dharmasena
What was the first Buddhist text to be translated into English? When was it translated and by whom? Was it reasonably available to those interested and did it have much of an impact within academic circles and perhaps to the wider culture?
What was the first Buddhist text to be translated into English?
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buddhism.stackexchange.com/users/157/Crab Bucket
These seem to be the first Buddhist texts ever translated into English, published in 1693:   THE LIFE OF THEVETAT , Translated from the Balie  (i.e. Pāli). As to the first  notable  translation, this honorary title GOES to  Max Muller's translation of Dhammappada , first published in  1869 , later included in Muller's  Sacred Books of the East  series published around  1880s .   The first Buddhist texts to be translated into English appear to be "The Life of Thevetat", from 1693. Other early translations include "The History and Doctrine of Buddhism", "An Explications of the Patimouc" and "Text of the Vinac". The first notable translation is credited to Max Muller's translation of Dhammappada, first published in  1869, later included in Muller's  Sacred Books of the East  series published around the 1880s, including some important suttas. Other notable translation work (in the  Theravada tradition ) has been done by  Thomas William Rhys Davids,  who founded the  Pali Text Society.
The first Buddhist texts to be translated into English appear to be "The Life of Thevetat", from 1693. Other early translations include "The History and Doctrine of Buddhism", "An Explications of the Patimouc" and "Text of the Vinac". The first notable translation is credited to Max Muller's translation of Dhammappada, first published in  1869, later included in Muller's  Sacred Books of the East  series published around the 1880s, including some important suttas. Other notable translation work (in the  Theravada tradition ) has been done by  Thomas William Rhys Davids,  who founded the  Pali Text Society.