score:6
Although I can find no evidence that H.P.Lovecraft understood French, he was accomplished enough in Latin to translate texts and, judging by this letter cited in Classical Traditions in Modern Fantasy, not unfamiliar with the spoken language either:
Latin and Greek were my delight - although I had long-standing feud with teachers of the former over pronunciation. My grandfather had previously taught me a great deal of Latin, using the traditional English pronunciation taught in his day, but at school I was expected to follow the "Roman method"...
Lovecraft started learning Latin from his grandfather in 1898 when he was eight years old. By 1902 (by S. T. Joshi's estimate), he had translated "the first eighty-eight lines of Ovid’s Metamorphoses." He also had at least some knowledge of Greek as An H. P. Lovecraft Encyclopedia (p209) says
HPL’s surviving juvenile poetry consists largely of imitations or translations of Greek and Latin epics
(note: this thread says Joshi describes Lovecraft's Greek as rubbish, but I've been unable to confirm this)
Joshi, in A Visionary and A Dreamer: H. P. Lovecraft in his Time, further states:
In 1908 Lovecraft stood at the threshold of adulthood: he was doing reasonably well at Hope Street High School, he had become prodigiously learned in chemistry, geography, astronomy, and meteorology, and he was accomplished in belles-lettres as a Latinist, poet, and fiction writer.
Franz Rottensteiner, in a review of another Joshi book, H.P. Lovecraft: The Decline of the West, casts some doubt as the extent of Lovecraft's Latin, but at the same time indicates some knowledge of Spanish:
He had almost no formal education and was almost entirely self-taught. Even though he was able to formulate Latin sentences and correct the Spanish grammar of his correspondents, it seems less than probable that he was sufficiently fluent in any language other than English to read books on difficult philosophical subjects published in that language.
Upvote:5
The biographies of H.P Lovecraft all indicate that his education was interrupted by periods of illness. Also, as @T.E.D. noted above, he lived his entire life in the northeast United States, and probably had limited opportunities for interaction with non-English speakers.
Although I haven't been able to locate any document that explicitly states that Lovecraft was monolingual, I was able to locate references to a letter written by Lovecraft to Robert E. Howard, dated 29 March 1933, in which he states:
"... I am abysmally weak in modern languages, and mathematics, and in certain phases of history ...".
The letter is apparently published in the collection A Means to Freedom: The Letters of H. P. Lovecraft and Robert E. Howard, edited by S. T. Joshi, David E. Schultz, and Rusty Burke.
Given the above, it seems likely that Lovecraft was essentially monolingual.