Translation in SAPscript

SAPscript...
/*   Text Shells 
/: DEFINE &CUST_TXT&          = 'CUST#'
/: DEFINE &VAT_TXT&           = 'VAT_NUM'
/*   Calculation Shells 
/: PERFORM  FIXED_TEXT IN PROGRAM ZZ_ES_SD_INVOICE
/: USING &NAST-SPRAS&
/: USING &CUST_TXT&
/: USING &VAT_TXT&
/: CHANGING &CUST_TXT&
/: CHANGING &VAT_TXT&
/: ENDPERFORM
abap:
 form fixed_text tables inttab structure itcsy
                        outtab structure itcsy.
   data:   lt_language like sy-langu,
           lt_iso      like t002-laiso,
           ln_tabix    like sy-tabix,
  read table inttab index 1.

  if sy-subrc eq 0.
    lt_iso = inttab-value.
    call function 'LANGUAGE_CODE_ISO_TO_SAP'
         exporting
              iso_code  = lt_iso
         importing
              sap_code  = lt_language
         exceptions
              not_found = 1
              others    = 2.
    if sy-subrc <> 0.
      "do nothing - it will pick up English by default
    endif.
  endif.

  describe table inttab lines ln_lines.
  if ln_lines < 2.
    exit.
  endif.
  loop at inttab from 2.
    read table outtab with key name = inttab-name.
    read table outtab with key name = inttab-name.
    if sy-subrc ne 0.
      continue.
    else.
      ln_tabix = sy-tabix.
    endif.

    perform svs_read_znfixtext using    inttab-value
                                        lt_language
                               changing outtab-value.
    modify outtab index ln_tabix.

  endloop.

endform.                                  " FIXED_TEXT