The Russian language has 10 (!) single-letter words
These letters are prepositions, conjunctions and pronouns.
‘А’ is not just a letter, but a conjunction. ‘Я’ (‘Ya’) is a pronoun. In total, there are 10 words in Russian that consist of just one letter! Besides ‘A’ and ‘Я’, these are ‘Б’ (‘B’) (particle), ‘В’ (‘V’) (preposition), ‘Ж’ (‘Zh’) (particle), ‘И’ (‘I’) (conjunction), ‘К’ (preposition), ‘О’ (conjunction), ‘С’ (‘S’) (conjunction), ‘У’ (‘U’) (preposition).