Here are a few quotations from great thinkers as to the need for an auxiliary language: 

   The diversity of languages is fatal for genius and progress.  If
   there were a universal language, we should save a third of life. 
   (Leibnitz.)

   The interrelationships of the peoples are so great that they most
   certainly need a universal language. (Montesquieu.)

   One of the greatest torments of life is the diversity of language. 
   (Voltaire.)

   What an immeasurable profit it would be for the human race if we were
   able to intercommunicate by means of one language. (Volney.)

   It seems to me quite possible—­probable even—­than an artificial
   language to be universally used will be greed upon. (Herbert
   Spencer.)

The learning of many languages fills the memory with words instead of facts and thoughts, and this is a vessel which, with every person, can only contain certain limited amount of records.  Therefore the learning of many languages is injudicious, inasmuch as it arouses the belief in the possession of dexterity, and, as a matter of fact, it lends a kind of delusive importance to social intercourse.  It is also injurious in that it opposes the acquirement of solid knowledge and the intention to win the respect of men in an honest way.  Finally, it is the ax which is laid at the root of a delicate sense of language in our mother tongue, which thereby is incurably injured and destroyed.  The two nations which have produced the greatest stylists, the Greeks and the French, learned no foreign languages; but as human intercourse grows more cosmopolitan, and as, for instance, a good merchant in London must now be able to read and write eight languages, the learning of many tongues has certainly become a necessary evil; but which, when finally carried to an extreme, will compel mankind to find a remedy, and in some far off future there will be a new language used at first as a language of commerce, then as a language of intellectual intercourse, then for all, as surely as some time or other there will be aviation.  Why else should philology have studied the laws of language for a whole century and have estimated the necessary, the valuable, and the successful portion of each separate language? (Nietsche.)

In this connection it may be well to repeat once more that Esperanto is only an “auxiliary” language.  Nobody dreams of it being a “universal language.”

Examplesof Esperanto.

Simpla, fleksebla, belsona, vere internacia en siaj elementoj[1], la lingvo Esperanto prezentas al la mondo civilizita la sole veran solvon[2] de lingvo internacia:  cxar[3], tre facila por homoj nemulte instruitaj, Esperanto estas komprenata sen peno de la personoj bone edukitaj.  Mil faktoj atestas la meriton praktikan de la nomita lingvo.

   [1] “j” has the sound of English “y”, as in boy, and is the sign for
   the plural of nouns and adjectives.