Unlike nouns and verbs, pronouns usually evolve glacially. Anglophones have been using their tidy little set for centuries. But change is not impossible. In Sweden “hen”, a gender-neutral pronoun, ...

The indefinite pronouns algún and ningún need to agree in gender (when possible) and in number with the noun they are substituting. Algo and alguien are not gender or number specific. algún ...

They clearly forgot that singular you was a plural pronoun that had become singular as well. You functioned as a polite singular for centuries, but in the 17th century, singular you replaced thou ...