追踪代码发现function都在这里， SD_ORDER_CREDIT_RELEASE
RVALVFORMS
CALL FUNCTION 'MESSAGE_TEXT_BUILD'
EXPORTING
msgid = sy-msgid
msgnr = sy-msgno
msgv1 = sy-msgv1
msgv2 = sy-msgv2
msgv3 = sy-msgv3
msgv4 = sy-msgv4
IMPORTING
message_text_output = news-text.