When applying for Canadian citizenship, am I required to attach a proof of language? What is a Language Proof?

A Language Proof is used to confirm that you have reached a sufficient level of English or French. You must submit a Language Proof if you are 18 to 54 years old at the time of sending your application, even if your first language is English or French. 

Several documents are accepted:

• A diploma, certificate or transcript from a program of study proving that you have studied in English or French.
• Results of a third-party assessment test. More details on assessment tests.

Report cards from a government-funded linguistic program where you achieved 4 (CLB/NCLC) or higher. In Quebec, this program is called the Francization Program of the Ministère de l’Immigration, de la Francisation et de l’Intégration (MIFI).