public static boolean isAlphabetic(char[] token, int length) {
        for (int i = 0; i < length; i++) {
            int cp = token[i];
            if (Character.isHighSurrogate(token[i])) {
                if (i < length - 1) {
                    cp = Character.toCodePoint(token[i], token[i + 1]);
                    i++;
                }
            }
            if (Character.isDigit(cp)) {
                return false;
            }
            if (!Character.isAlphabetic(cp) && !Character.isIdeographic(cp) && cp != UNDERSCORE) {
                return false;
            }
        }
        return true;
    }
Factory for filter that only allows tokens with characters that "isAlphabetic"  or "isIdeographic" through.
tika-eval/tika-eval-core/src/main/java/org/apache/tika/eval/core/tokens/AlphaIdeographFilterFactory.java