Spelling out numbers in words (Dutch)

Here’s an algorithm (in pseudo-code) for spelling out numbers in Dutch words (e.g. convert 123 to "honderddrieëntwintig"):

-- spell out an integer number in words (Dutch)
function numberToWordsDutch(number)
  var result, iteration, iterationText, hundreds, hundredsText

  if number = 0
    return "nul"
  end
  
  result ← ""
  iteration ← 1
  
  -- iterate per 3 digits (starting with last)
  while number > 0
    hundreds ← number modulo 1000 -- e.g. 23456 → 456
    number ← floor(number / 1000) -- e.g. 23456 → 23
    
    if hundreds > 0
      -- 3 digits to text
      hundredsText ← getHundredsText(hundreds)
      if iteration > 1
        -- duizend, miljoen, …
        iterationText ← getIterationText(iteration)
        hundredsText ← hundredsText + iterationText
        if hundredsText = "eenduizend "
          hundredsText ← "duizend "
        end
      end
      
      result ← hundredsText + result
    end
    
    iteration ← iteration + 1
  end
  
  return trim(result)
end

function getHundredsText(number)
  var result, hundreds, tens
  
  result ← ""
  
  hundreds ← floor(number / 100) -- e.g. 456 → 4
  if hundreds > 0
    number ← number modulo 100 -- e.g. 456 → 56
    if hundreds > 1
      result ← result + getLessThanTwentyText(hundreds)
    end
    result ← result + "honderd"
  end
  
  if number > 0
    if hundreds > 0 and number ≤ 12
      result ← result + "en"
    end
    
    if number < 20
      -- < 20 ⇒ look up
      result ← result + getLessThanTwentyText(number)
    else
      tens ← floor(number / 10) -- e.g. 42 → 4
      number ← number modulo 10 -- e.g. 42 → 2
      
      if number > 0
        -- een, twee, drie, …
        result ← result + getLessThanTwentyText(number)
        if number = 2 or number = 3
          result ← result + "ën"
        else
          result ← result + "en"
        end
      end
      
      -- dertig, veertig, …
      result ← result + getTensText(tens)
    end
  end
  
  return result
end

function getLessThanTwentyText(number)
  case number
    when 1 return "een"
    when 2 return "twee"
    when 3 return "drie"
    when 4 return "vier"
    when 5 return "vijf"
    when 6 return "zes"
    when 7 return "zeven"
    when 8 return "acht"
    when 9 return "negen"
    when 10 return "tien"
    when 11 return "elf"
    when 12 return "twaalf"
    when 13 return "dertien"
    when 14 return "veertien"
    when 15 return "vijftien"
    when 16 return "zestien"
    when 17 return "zeventien"
    when 18 return "achttien"
    when 19 return "negentien"
    otherwise error
  end
end

function getTensText(tens)
  case tens
    when 2 return "twintig"
    when 3 return "dertig"
    when 4 return "veertig"
    when 5 return "vijftig"
    when 6 return "zestig"
    when 7 return "zeventig"
    when 8 return "tachtig"
    when 9 return "negentig"
    otherwise error
  end
end

function getIterationText(iteration)
  case iteration
    when 1 return ""
    when 2 return "duizend "
    when 3 return " miljoen "
    when 4 return " miljard "
    when 5 return " biljoen "
    when 6 return " biljard "
    when 7 return " triljoen "
    when 8 return " triljard "
    otherwise return " ??? "
  end
end