How to remove accentuation?

To handle this in the general case, you would decompose the string, then strip out non-spacing marks. Unicode normalization has been requested previously, and will hopefully make it into the product at some point.

Another option is to use a regular expression, like this:

ClassMethod ReplaceAccents(ByRef pWord As %String) As %Status
{
  Set tSC = $$$OK
  Try {
      Set dictionary = ##class(%ArrayOfDataTypes).%New()
      Do dictionary.SetAt("ÀÁÂÃÄÅ","A")
      Do dictionary.SetAt("àáâãäå","a")
      Do dictionary.SetAt("ÈÉÊË","E")
      //.... all the rest
   
      While dictionary.GetNext(.key) {
        Set matcher = ##class(%Regex.Matcher).%New("["_ dictionary.GetAt(key) _ "]", pWord)
        Set pWord = matcher.ReplaceAll(key)
      }
  } Catch tException {
    Set:$$$ISOK(tSC) tSC = tException.AsStatus()
  }
  Quit tSC
}

This is a very delayed answer to an old question, but there is now a $zconvert mode in IRIS that will do this for you:

> write $zconvert("Árvore", "A")

Arvore