Learn Portuguese (Portugal): Sim, ele é inglês.

In Portuguese, words for nationalities and languages are written with a lowercase letter unless they are at the beginning of a sentence. So, 'English' becomes inglês.

How would I change this sentence to ask 'Is he English?'

You keep the exact same word order! Unlike English, which swaps the verb and subject to ask a question, Portuguese keeps the standard Subject-Verb-Object order: Ele é inglês? You simply raise the pitch of your voice at the end to show it is a yes/no question.

Why do we use é here instead of está?

Both mean 'is', but we use é (from the verb ser) for permanent traits, such as someone's nationality, identity, or origins. We use está (from estar) for temporary states or locations.

What do the different accents on é and inglês mean?

The acute accent on é shows it has an 'open' vowel sound, similar to the 'e' in the English word 'pet'. The circumflex (little hat) on inglês shows a 'closed' vowel sound, and also tells you to put the stress on that final syllable.