When trying to replace two character with one the application crashes. It works fine with one character replacement

tt = new TextWatcher() { public void afterTextChanged(Editable s){ et.setSelection(s.length());

            }
            public void beforeTextChanged(CharSequence s,int start,int count, int after){}
            public void onTextChanged(CharSequence s, int start, int before, int count) {
                et.removeTextChangedListener(tt);
                String tvalue = et.getText().toString();
                tvalue = tvalue.replaceAll("k", "ક");;

//THE ABOVE line replaces "k" with "ક" WORKS FINE BUT THE BELOW replacing "કh" with "ખ" DOES NOT. IT CRASHES

                tvalue = tvalue.replaceAll("કh", "ખ");

      et.addTextChangedListener(tt);
            }
        };
        et.addTextChangedListener(tt);
    }