Spannable not highlighting a word inside large text that is persian

Question

Im trying to have a search function for a text view that shows a large text so when ever the user enters a word the word would be highlighted inside the text view and my code does work with english but not with persian.

my highlighting method

 public void setHighLightedText(TextView tv, String textToHighlight) {
        String tvt = tv.getText().toString();
        int ofe = tvt.indexOf(textToHighlight, 0);
        Spannable wordToSpan = new SpannableString(tv.getText());
        for (int ofs = 0; ofs < tvt.length() && ofe != -1; ofs = ofe + 1) {
            ofe = tvt.indexOf(textToHighlight, ofs);
            if (ofe == -1)
                break;
            else {
                // set color here
                wordToSpan.setSpan(new BackgroundColorSpan(0xFFFFFF00), ofe, ofe + textToHighlight.length(), Spannable.SPAN_EXCLUSIVE_EXCLUSIVE);
                tv.setText(wordToSpan, TextView.BufferType.SPANNABLE);
            }
        }
    }

my TextView source

 @RequiresApi(api = Build.VERSION_CODES.KITKAT)
    private void GetText(int rawRes) {
        InputStream inputStream = null;
        try {
            inputStream = getResources().openRawResource(rawRes);
        } catch (Resources.NotFoundException e) {
            e.printStackTrace();
        }

        ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
        byte[] buffer = new byte[1024];
        int length;
        try {
            while ((length = inputStream.read(buffer)) != -1) {
                byteArrayOutputStream.write(buffer, 0, length);
            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                inputStream.close();
                byteArrayOutputStream.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }


        resultString = byteArrayOutputStream.toString();
    }

and my onCreate

        et = (EditText) findViewById(R.id.et);
        tv = (TextView) findViewById(R.id.tv);

        GetText(R.raw.largetext);


        tv.setText(resultString);

        next = (Button) findViewById(R.id.button1);
        next.setOnClickListener(new View.OnClickListener() {

            public void onClick(View v) {

                setHighLightedText(tv,et.getText().toString());


            }
        });

layout

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context=".activity.AboutUs">
    <EditText
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/et"/>
    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="find"
        android:id="@+id/button1"/>
    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/tv"/>

</LinearLayout>

Main text

```لورم ایپسوم یا طرح‌نما (به انگلیسی: Lorem ipsum) به متنی آزمایشی و بی‌معنی در صنعت چاپ، صفحه‌آرایی و طراحی گرافیک گفته می‌شود. طراح گرافیک از این متن به عنوان عنصری از ترکیب بندی برای پر کردن صفحه و ارایه اولیه شکل ظاهری و کلی طرح سفارش گرفته شده استفاده می نماید

phrase i want to search

لورم