I played around a but and the following file seems to work for WikkaWiki http://wikkawiki.org/HomePage.

Just create this file in the core directory and name it wiki_wikka_api.php.
And in your config_inc.php set:

Wiki Engine (supported engines: 'dokuwiki', 'mediawiki', 'wikka', 'xwiki')

$g_wiki_engine = 'wikka';

And point to your Wikka install.
That's it.

<?php

Mantis - a php based bugtracking system

Copyright (C) 2000 - 2002 Kenzaburo Ito - kenito@300baud.org

Copyright (C) 2002 - 2007 Mantis Team - mantisbt-dev@lists.sourceforge.net

Mantis is free software: you can redistribute it and/or modify

it under the terms of the GNU General Public License as published by

the Free Software Foundation, either version 2 of the License, or

(at your option) any later version.

#

Mantis is distributed in the hope that it will be useful,

but WITHOUT ANY WARRANTY; without even the implied warranty of

MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the

GNU General Public License for more details.

#

You should have received a copy of the GNU General Public License

along with Mantis. If not, see http://www.gnu.org/licenses/.

# --------------------------------------------------------
# $Id: wiki_wikka_api.php,v 1.0 2008-01-21 22:35:49 rstens Exp $
# --------------------------------------------------------

# ----------------------
# Gets the URL for the page with the specified page id.  This function is used
# internally by this API.
function wiki_wikka_get_url_for_page_id( $p_page_id ) {

    $p_page_id = ucfirst( $p_page_id );
    $t_root_url = config_get_global( 'wiki_engine_url' );

    $t_root_namespace = ucfirst(config_get( 'wiki_root_namespace' ));

    if ( is_blank( $t_root_namespace ) ) {
        $t_page_id = $p_page_id;
    } else {
        $t_page_id = $t_root_namespace . $p_page_id;
    }

    return $t_root_url . 'wikka.php?wakka=' . urlencode( $t_page_id );
}

# ----------------------
# Gets the page id for the specified issue.  The page id can then be converted
# to a URL using wiki_wikka_get_url_for_page_id().
function wiki_wikka_get_page_id_for_issue( $p_issue_id ) {
    $c_issue_id = ucfirst( db_prepare_int( $p_issue_id ));

    $t_project_id = bug_get_field( $p_issue_id, 'project_id' );
    $t_project_name = ucfirst( project_get_name( $t_project_id ));

    # create a namespace for the project to contain all project documentation.
    # create within it a namespace for issues.  This is to allow the creation of a _template.txt
    # file to act as the template for issues belonging to this project.
    return $t_project_name . 'Issue' . $c_issue_id;
}

# ----------------------
# Gets the page url for the specified issue id.
function wiki_wikka_get_url_for_issue( $p_issue_id ) {
    return wiki_wikka_get_url_for_page_id( wiki_wikka_get_page_id_for_issue( $p_issue_id ) );
}

# ----------------------
# Gets the page id for the specified project.  The project id can be ALL_PROJECTS
# The page id can then be converted to URL using wiki_wikka_get_url_for_page_id().
function wiki_wikka_get_page_id_for_project( $p_project_id ) {
    $t_home = 'Start';
    if ( $p_project_id == ALL_PROJECTS ) {
        return $t_home;
    } else {
        $t_project_name = project_get_name( $p_project_id );
        return ucfirst( $t_project_name ) . $t_home;
    }
}

# ----------------------
# Get URL for the specified project id.  The project is can be ALL_PROJECTS.
function wiki_wikka_get_url_for_project( $p_project_id ) {
    return wiki_wikka_get_url_for_page_id( wiki_wikka_get_page_id_for_project( $p_project_id ) );
}

?>