He who is ignorant of foreign languages, knows not his own.

[Wer fremde Sprachen nicht kennt, weiß nichts von seiner eigenen.]

Johann Wolfgang von Goethe (1749-1832) German poet, statesman, scientist

Über Kunst und Alterthum (1821)
    (Source)

Alt. trans.:

• "He who knows not foreign languages, knows nothing of his own."
• "No man who knows only his own language knows even that."
• "He who knows but one language knows none."
• "He who knows one language, knows none."
• "A man who has no acquaintance with foreign languages knows nothing of his own." [tr. Bailey Saunders]