My paternal grandfather knew 21 languages.
Jack (Battiscombe Gunn Gunn-1707 ,
https://en.wikipedia.org/wiki/Battiscombe_Gunn ) was an Egyptologist, specializing in the Ancient Egyptian language (there is even a rule of Ancient Egyptian grammer, Gunn's Rule, named after him). He taught himself to read heiroglyphs as a schoolboy, and then took some classes from Margaret Murray, at University College, London. He had gone to English "public" (i.e . private boarding) school, but a change in fanily finances meant he didn't go to University. None the less, in 1934 (when he was 51) Oxford University gave him an hororary M.A, and appointed him Professor of Egyptology.
He knew most of the modern European languages (German, Italian, French, etc.), the languages of the modern Near East (including Arabic and Coptic) most of the classical languages (Latin, Greek, Hebrew, Aramaic, Sanscrit, etc), and many of the ancient langauges, some of which only exist in written form, and nobody knows how they were atually spoken (Ancient Egyptian, Hittite, Sumerian, etc.).
My father (Jack's son) once asked him how many languages he knew. First they had to decide on a definition of "knowing a language", and agreed on "read, write, and speak where spoken" (since some of the Ancient languages are no longer spoken).
The answer, after some consideration, was that Jack knew 21 languages.
That did NOT include Spanish (he would read Cervantes (author of Don Quixote) in the original, and he could write a business letter in Spanish, but he was not fluent in conversation), or the various languages he "learned" from missionary bibles.
One of the missionary societies published bibles in the languages of the people they were trying to convert. They expanded to publishing bibles in all sorts of languages, even ones that were not related to their missionary work. Jack used to get lumbago (fancy word for lower back pain) each winter, and would be bedridden for several weeks. While in bed he would use one of these missionary bibles to earn how to read a new language. But he could neither write nor speak those languages, so they did not count.