spanish_sort.rb

strings = %w[aa áb ac na ña ne oa]

# Provide alphabetical sort in Spanish, where accented vowels are sorted
# the same as unaccented vowels, and "ñ" is sorted directly after "n".
#
# This is accomplished by normalizing the string to Unicode decomposed form
# to break characters with diacritics into multiple characters, and then
# removing acute accents and diaresis: e.g. "á" becomes "a", "ü" becomes
# "u". These are the only two diacritics used for vowels in Spanish.
#
# The tilde is left on the "ñ", which allows the meals to be alphabetized
# correctly with "ñ" between "n" and "o".
def spanish_sort(array)
  array.sort do |a, b|
    a.unicode_normalize(:nfd).delete("\u0301\u0308") <=> b.unicode_normalize(:nfd).delete("\u0301\u0308")
  end
end

pp strings.sort          #=> ["aa", "ac", "na", "ne", "oa", "áb", "ña"]
pp spanish_sort(strings) #=> ["aa", "áb", "ac", "na", "ne", "ña", "oa"]