Yes, all candidates need to take a language test in order to determine their language abilities. There are a set number of points available for language ability for each of the economic immigration programs that come under Express Entry, and ability must be proven by candidates taking a standardized language test approved by Immigration, Refugees and Citizenship Canada (IRCC, formerly known as CIC). The most popular are IELTS, CELPIP for English and TEF or TCF Canada for French.
As part of their Express Entry profile, candidates must submit valid language test results obtained in the past two years. Once a candidate enters the Express Entry pool, he or she can earn extra points and increase his or her rank by taking another language test and obtaining better results. As of June 6, 2017, additional points are also available to candidates who prove French language ability in addition to English language ability. Candidates can practice IELTS before taking the test.