This article is from the Esperanto FAQ, by Mike Urban firstname.lastname@example.org and Yves Bellefeuille email@example.com with numerous contributions by others.
About 75 % of Esperanto's vocabulary comes from Latin and Romance
languages (especially French), about 20 % comes from Germanic languages
(German and English), and the rest comes mainly from Slavic languages
(Russian and Polish) and Greek (mostly scientific terms).
The words derived from Romance languages were chosen to be as
recognizable as possible throughout the world. For example, the word
"radio", although technically Romance, is now used internationally.
Someone knowing only Russian and looking at a text in Esperanto would
immediately recognize perhaps 40 % of the words, without even having
studied the language.
Esperanto is phonetic: every word is pronounced exactly as it is
spelled. There are no "silent" letters or exceptions.