For the first step of the application no language certificates are required. However, when you apply at the host university a proof of your language ability might be required, e.g., a certain grade in English in the Abitur. Please note: not all universities require this.
IMPORTANT: If you are not a EU/EEA citizen you will have to apply for a Tier 4 visa. For this purpose, you need to prove your language skills by presenting an official language certificate.