Leeuwenhoek's Death

In the final year of his long life, Leeuwenhoek wrote five letters and had them all translated into Latin before he sent them. Other than the 1679 letter about human sperm and the letter of January 15, 1721, these were the only letters published in Latin in Philosophical Transactions. However, for the thirty years he self-published his collected letters, they were all translated into Latin, so he certainly had access to translators.

His friend, publisher Reinier Boitet, described the scene (Dobell translation):
Six-and-thirty hours before his death, when his limbs were already growing numb, the fire of his ardour glowed still so bright, that, with lips stammering and well-nigh stiff, he directed his thoughts to be set down on paper regarding a kind of sand which a certain distinguished gentleman, a director of the East-India Company, had handed over to him, to find out whether any gold were concealed therein.
Leeuwenhoek summoned his friend Johan Hoogvliet, who wrote in his cover letter to Philosophical Transactions editor James Jurin:
Our venerable old van Leeuwenhoek, being already in the throes of death, though none the less mindful of his art, ordered me to be called to him; and raising his eyes, now heavy with death, kept asking me in half-broken words if I would translate these two letters out of our native tongue into Latin, and send them, most distinguished Sir, to you.
Jurin published them, in Latin, along with Hoogvliet's cover letter, in volume 32.
Leeuwenhoek died in Delft on August 26, 1723, just shy of his 91st birthday, of bronchial pneumonia.