Sometimes you don't want to define a new label environment or
macro, but just change the information associated with a label
category. Maybe you want to add some magic words, for another
language. Changing only the information associated with a label
category is done by giving nil for the environment
name and then specify the items you want to define. Here is an
example which adds German magic words to all predefined label
categories.
(setq reftex-label-alist
'((nil ?s nil nil nil ("Kapitel" "Kap." "Abschnitt" "Teil"))
(nil ?e nil nil nil ("Gleichung" "Gl."))
(nil ?t nil nil nil ("Tabelle"))
(nil ?f nil nil nil ("Figur" "Abbildung" "Abb."))
(nil ?n nil nil nil ("Anmerkung" "Anm."))
(nil ?i nil nil nil ("Punkt"))))