Anyone aged 18-65 must demonstrate English to the required level for ILR. The minimum level is (B1) of the CEFR framework, in both Speaking and Listening.
If the applicant is the majority of an English language speaking country, they can show evidence of their nationality, to prove that they meet the requirement.
Other applicants need to supply evidence that they have either a Home Office approved English test result or have a degree taught in English. Degrees taught outside the UK will need to be accompanied by a  UK ENICcertificate showing the academic level and, where applicable, the English language level at which the degree was taught.