public boolean isLetter(int c) {
        if (Character.isLetter(c)) return true;
        if (Character.isDigit(c) &&  ! isLatin(c)) return true; // Not considering these digits, so treat them as letters

        // Some CJK punctuation defined as word characters
        if (c == '\u3008' || c == '\u3009' || c == '\u300a' || c == '\u300b' ||
            c == '\u300c' || c == '\u300d' || c == '\u300e' ||
            c == '\u300f' || c == '\u3010' || c == '\u3011') {
            return true;
        }
        int type = java.lang.Character.getType(c);
        return type == java.lang.Character.NON_SPACING_MARK ||
               type == java.lang.Character.COMBINING_SPACING_MARK ||
               type == java.lang.Character.ENCLOSING_MARK;
    }
Returns true for code points which are letters in unicode 3 or 4, plus some additional characters
which are useful to view as letters even though not defined as such in unicode.
linguistics/src/main/java/com/yahoo/language/process/CharacterClasses.java