You need to add following lines on custom_config.php
// can be number or letters but have to be defined AS A SINGLE CHARACTER due to DB SCHEMA
// define('TL_REQ_STATUS_MUST', 'MU'); KO !!! will result in TL CRASH
define('TL_REQ_STATUS_MUST', 'M');
define('TL_REQ_STATUS_SHOULD', 'S');
define('TL_REQ_STATUS_COULD', 'C');
define('TL_REQ_STATUS_WONT', 'T');
$tlCfg->req_cfg = new stdClass();
$tlCfg->req_cfg->status_labels = array(TL_REQ_STATUS_MUST => 'req_status_must',
TL_REQ_STATUS_SHOULD => 'req_status_should',
TL_REQ_STATUS_COULD => 'req_status_could',
TL_REQ_STATUS_WONT => 'req_status_wont');
You also need to define YOUR strings.txt file to have TRANSLATION for:
'req_status_must', 'req_status_should', 'req_status_could', 'req_status_wont'
Example for english
on [YOUR TL INSTALLATION]/locale/en_GB/custom_strings.txt
$TLS_req_status_must = "Must";
$TLS_req_status_should = "Should";
$TLS_req_status_could = "Could";
$TLS_req_status_wont = "Will Not";