RTEditor/src/main/java/com/onegravity/rteditor/utils/Helper.java
public static boolean isRTL(CharSequence s, int start, int end) {
        if (s == null || s.length() == 0) {
            // empty string --> determine the direction from the default language
            return isRTL(Locale.getDefault());
        }

        if (start == end) {
            // if no character is selected we need to expand the selection
            start = Math.max(0, --start);
            if (start == end) {
                end = Math.min(s.length(), ++end);
            }
        }

        try {
            Bidi bidi = new Bidi(s.subSequence(start, end).toString(), Bidi.DIRECTION_DEFAULT_LEFT_TO_RIGHT);
            return ! bidi.baseIsLeftToRight();
        }
        catch (IndexOutOfBoundsException e) {
            return false;
        }
    }
public static boolean isRTL(CharSequence s, int start, int end) {
        if (s == null || s.length() == 0) {
            // empty string --> determine the direction from the default language
            return isRTL(Locale.getDefault());
        }

        if (start == end) {
            // if no character is selected we need to expand the selection
            start = Math.max(0, --start);
            if (start == end) {
                end = Math.min(s.length(), ++end);
            }
        }

        try {
            Bidi bidi = new Bidi(s.subSequence(start, end).toString(), Bidi.DIRECTION_DEFAULT_LEFT_TO_RIGHT);
            return ! bidi.baseIsLeftToRight();
        }
        catch (IndexOutOfBoundsException e) {
            return false;
        }
    }
This method determines if the direction of a substring is right-to-left.
If the string is empty that determination is based on the default system language
Locale.getDefault().
The method can handle invalid substring definitions (start > end etc.), in which case the
method returns False.

@return True if the text direction is right-to-left, false otherwise.