looking for a linguistical/semiotic quote

[Vlastimil Brom]

2013/6/27 rusi <rustompmody at gmail.com>:
> I am looking for a quote
> (from Whorf/Sapir/Wittgenstein/Humboldt dunno... that 'school')
>
> It goes something like this:
>
> What characterizes a language is not what we can say in it but what we must -- like it or not -- say.
> [...]

Hi,
I belive, the author is Roman Jakobson, see the respective post about
this very question:
http://linguistlist.org/issues/9/9-32.html

There seem to be several variations,
Another remarkable linguist Eugenio Coseriu mentions this in his paper
(Sprache: Strukturen und Funktionen ... Tübingen 1979, p. 119).
The German text is besides mentioning Jakobson almost fully equivalent
to you original quote:
"R. Jakobson bemerkt mit Recht, daß sich die Sprachen nicht durch das,
was sie sagen können, unterscheiden, sondern durch das, was sie sagen
müssen."

http://books.google.cz/books?id=JkGCkC8RYcEC
p. 119

hth,
  vbr