Highlighting searched word and its meaning in c#

Assume: a WinForms project where:

1. Controls

Button: btnTranslate: click to translate English to Arabic: uses rtbEnglish, rtbArabic
Button: btnSearchButton: click to search for an English word: uses tbSearchEnglish

RichTextBox: rtbEnglish: displays user-entered English text
RichTextBox: rtbArabic: displays English text in rtbEnglish translated into Arabic
TextBox: tbSearchEnglish: displays user-entered English text, to used to search

2. Run-time behavior: Translate

a. When the btnTranslate is clicked: text in rtbEnglish is checked for a valid entry, and if valid:

b. is processed into an Array or generic List of strings; and:

c. the rtbArabic RichTextBox is cleared, and: a word-by-word look-up of each English word in the database is performed which returns a corresponding Arabic word(s) which is then appended to the rtbArabic RichTextBox Text.

3. Run-time behavior: Search

a. tbSearch is parsed for a valid entry (can it have more than one word ?), and, if valid:

b. occurrence of any of the word(s) in the rtbEnglish is highlighted, and their corresponding words in rtbArabic are highlighted.

4. Run-time behavior: user edits rtbEnglish

a. rtbArabic is cleared, any highlights in rtbEnglish are removed ?

5. Strategy:

a. since no run-time editing is allowed without re-translation, then, when the translation is performed word-by-word, you can know the position (start, and end) of each English word, and you can know the position of each Arabic word/phrase inserted.

b. we can use Dictionaries: one to map English words to the Arabic translation, and two of type <string, List<int>> to hold a "mapping" of each English word to all its occurrences in both rtbEnglish, and rtbArabic RichTextBoxes.

// dictionary mapping English word to Arabic translation
Dictionary<string, string> dctEnglishToArabic = new Dictionary<string, string>();
    
// dictionaries mapping word to Locations
Dictionary<string, List<int>> dctEnglishWordToLocations = new Dictionary<string, List<int>>();

Dictionary<string, List<int>> dctArabicWordToLocations = new Dictionary<string, List<int>>();

6. Code: ... note this is an outline of code, not complete working code

// assume you have a function like: private string YourDataBaseLookUp(string englishWord);
// that takes an English word as a parameter, and returns a string which
// contains the Arabic translation

// characters to ignore in the English text
private char[] charsToSplit = new char[] {' ', '\t', '\n'};     

// translate
private void btnTranslate_Click(object sender, EventArgs e)
{
    // get ready
    rtbArabic.Clear();
    dctEnglishToArabic.Clear(); 
    dctEnglishWordToLocations.Clear();
    dctArabicWordToLocations.Clear();

    // create the list of English words
    List<string> englishWords = rtbEnglish.Text.Split(charsToSplit, StringSplitOptions.RemoveEmptyEntries).ToList();

    // keep track of where we are in content
    int englishNdx = 0;
    int arabicNdx = 0;

    // build the Dictionary that maps words to locations

    string theArabic = "";

    foreach (string s in englishWords)
    {
        // repeat of word ? we already have a translation
        if (dctEnglishWordToLocations.Contains(s))
        {
            // what do you need to do here
            // to add the new start location
            // to the location dictionaries ?
            // and update the indexes ?
        }
        else
        {
            // length of the English word
            int eLen = s.Length;

            // new word
            theArabic = YourDataBaseLookUp(s);

            // length of the Arabic translation
            int aLen = theArabic.Length;

            dctEnglishToArabic.Add(s, theArabic);

            // what do you need to do to calculate the location
            // using the index variables and length of the strings ?
            // what do you need to do to update the index variables ?

            // you initialize the location lists in each dictionary here
            dctEnglishWordToLocations.Add(s, new List<int>());
            dctArabicWordToLocations.Add(s, new List<int>());

            // then: what do you need to do to insert the location
            // of the new word into the location dictionaries ?
        }
    }
}
// search
private void btnSearch_Click(object sender, EventArgs e)
{
    // get a list of the words in tbSearch
    // List<string> searchWords = ????;</string>
    
    // go through the list
    foreach(string wrd in searchWords
    {
       List<int> eLocations = dctEnglishWordToLocations[wrd];
       List<int> aLocations = dctArabicWordToLocations[wrd];

       // now use both lists, and perform the high-lighting in both
       // both rtbEnglish, and rtbArabic
    }
}

Note: A big problem not addressed here is that you will want to get the positions of the words in the English text by considering exactly where they occur (and that includes the white-space before them) in the rtbEnglish; I am not familiar with punctuation in Arabic, and do not know what issues you will face there.

Note: this "outline" has been done quickly; I'll revise it as I have time.

Note: A problem you will have to deal with here is when you have English text like this:

"An apple a day, will keep the doctor away, but, eating too many apples, like, for example, golden delicious apples, could make you sick."

What do you do to handle translating "apple" "apples" "apples," ?