Is this Andrew Joseph Planta, the German reformed pastor who arrived in 1753 to service the German colony, and in 1770 was eleced FRS? See DNB:
'After a period as professor of mathematics at Erlangen, Bavaria, Andrew Planta moved to England in 1752 with his wife and family, where he became minister of the German Reformed church in London. In 1758 he was appointed one of the assistant librarians of the recently founded British Museum, working in the department of natural and artificial productions until 1765, and then transferring to the department of printed books where he served until his death. He became a fellow of the Royal Society in 1770. He was buried at St George's, Bloomsbury, on 3 March 1773, where his daughter, Frederica Planta, English teacher to the young princes and princesses, was buried in February 1778.'