This is a short but important post. The word English must always be capitalized. Always. There are no exceptions (other than in billiards.)
This is true for both the noun English (the English language) and the adjective English (describing a person, place or thing associated with England or the English people.)
John speaks English and French.
I am American but my co-founder is English.
Chen is learning English so that he can move to San Francisco.
Why is it Capitalized?
Because it’s a proper noun. Proper nouns are always capitalized. English is a proper noun referring to the English language, or to something related to the specific country of England.
What is a Proper Noun?
A proper noun is a name used for an individual, specific, person, place, or thing. So, as stated above, English is a proper noun.