To use many words to communicate few thoughts is everywhere the unmistakable sign of mediocrity. To gather much thought into few words stamps the man of genius.

[Viele Worte machen, um wenige Gedanken mitzutheilen, ist überall das untrügliche Zeichen der Mittelmäßigkeit; das des eminenten Kopfes dagegen, viele Gedanken in wenige Worte zu schließen.]

Arthur Schopenhauer (1788-1860) German philosopher

Parerga and Paralipomena, Vol. 2, ch. 23 “On Authorship and Style [Über Schriftstellerei und Stil],” § 283 (1851) [tr. Saunders (1890)]
    (Source)

(Source (German)). Alternate translations:

The use of many words in order to express little thought is everywhere the infallible sign of mediocrity; while to clothe much thought in a few words is the infallible sign of distinguished minds.
[tr. Dircks (1897)]

To use many words for the purpose of conveying few ideas is everywhere the infallible sign of mediocrity; whereas that of an eminent mind is the inclusion of many ideas into few words.
[tr. Payne (1974)]