Loop through an array of single character strings, find consecutive characters, extract them, and insert them in the original array as a single string

I am creating a translator app of sorts and I am stuck on one little aspect. So far, I have a custom keyboard that creates a single string, then a function that takes that string and converts it to an array of characters:

@State var toBeTranslated = ""

// function added to custom keyboard buttons with corresponding characters
func addLetter(_ letter: String -> [String] {
    let stringArray = toBeTranslated.map{ String($0) }
    return stringArray
}

After the string is converted into an array of characters, the array is iterated through and each index is assigned to the string name of an Image to display on screen. The images are of special symbol for that letter:

// the WrappingHStack is used as the ForEach in this case
WrappingHStack(alignment: .leading, spacing: .dynamic(minSpacing: 15)) {
                    WrappingHStack(addLetter(toBeTranslated), id: \.self) { character in
                        Image(character)
                            .resizable()
                            .scaledToFit()
                            .frame(width: 30, height: 30)
                    }
                }

The issue I have now is the special characters for the letter combinations of "CH" "AE", "EO", "KH" "NG", "OO", "SH", and "TH". Meaning, if the word(s) has these letters consecutively, a single symbol will be represented instead of two.

For instance, if the user typed in "SMOOTH CHARACTER", instead of 15 symbols, there will be 12 as the "OO", "TH", and "CH" will all be replaced with the single symbol.

I've been trying different methods to identify these consecutive characters like this function:

func checkForConsecutiveCharacters(character1: String, character2: String, within stringArray: [String]) -> Bool {
        for index in stringArray.indices.dropLast() {
            if stringArray[index] == character1 && stringArray[index + 1] == character2 {
                return true
            }
        }
        return false
    }

I just can't get past this part.

Basically, I need to be able to iterate through the original array of single characters, identify if the consecutive characters above exist, then I need to either combine just those two character into a single string in the original array, or extract them, then combine them, then replace them with those two characters in the original array to display the corresponding symbol image.

i.e. end result of:

convert from:
["S", "M", "O", "O", "T", "H", " ", "C", "H", "A", "R", "A", "C", "T", "E", "R"]

convert to:
["S", "M", "OO", "TH", " ", "CH", "A", "R", "A", "C", "T", "E", "R"]

Thanks!

This is a solution which detects the special characters with regular expression. It walks thru the string by index. If a pattern is detected two characters are appended to the result otherwise only one. The current index is increased accordingly.

func convert(string: String) -> [String] {
    var result = [String]()
    let specialCharacterPattern = "^(CH|AE|EO|KH|NG|OO|SH|TH)"
    var currentIndex = string.startIndex
    while currentIndex < string.endIndex {
        let isSpecial = string[currentIndex...].range(of: specialCharacterPattern, options: .regularExpression) != nil
        var temp = String(string[currentIndex])
        currentIndex = string.index(after: currentIndex)
        if isSpecial {
            temp.append(string[currentIndex])
            currentIndex = string.index(after: currentIndex)
        }
        result.append(temp)
    }
    return result
}

print(convert(string: "SMOOTH CHARACTER"))