WPML doesn't properly handle field groups that are assigned to page parents. This filter fixes that.

Fix WPML + ACF Parent Page Location Issues

// Make WPML compatible with ACF field groups with location set to 'page parent'
function filter_acf_location_rule_match_param( $result, $rule, $screen, $field_group ) {
	$default_lang = apply_filters( 'wpml_default_language', NULL );

	if ( ! isset( $screen['lang'] ) || $default_lang == $screen['lang'] ) {
		return $result;
	}

	if ( ! isset( $screen['post_id'] ) || empty( $screen['post_id'] ) ) {
		return $result;
	}

	$default_lang_post_id = apply_filters( 'wpml_object_id', $screen['post_id'], $screen['post_type'], false, $default_lang );

	if ( ! $default_lang_post_id ) {
		return $result;
	}

	$default_lang_post_parent_id = wp_get_post_parent_id( $default_lang_post_id );

	if ( ! $default_lang_post_parent_id ) {
		return $result;
	}

	switch ( $rule['operator'] ) {
		case '==':
			if ( $default_lang_post_parent_id == $rule['value'] ) {
				$result = true;
			}
			break;

		case '!=':
			if ( $default_lang_post_parent_id != $rule['value'] ) {
				$result = true;
			}
			break;
	}

	return $result;
}; 
add_filter( 'acf/location/match_rule/type=page_parent', 'filter_acf_location_rule_match_param', 10, 4 );