Translation guide
To have faith, trust, or confidence in someone or something; to accept the existence or value of something.
I believe in him.
She believes in her team.
Can also mean 'believe in' a person, but often implies believing what they say or believing in their existence/qualities. Slightly less common for trust in abilities.
I believe in him. (I believe what he says / I have faith in him)
Expressing belief in the value, truth, or effectiveness of something abstract.
Expressing that you think something exists, such as ghosts, gods, or aliens.
Expressing self-confidence or faith in one's own abilities.
The standard phrase for 'believe in oneself'. Used in motivational contexts.
Believe in yourself.
He couldn't believe in himself.
Literally 'have self-confidence'. A very common alternative, often more natural in some contexts.
Believe in yourself more. (Have more confidence.)
信じる (shinjiru) is broader: it can mean believe in existence, truth, or value. 信頼する (shinrai suru) specifically means trust in reliability, ability, or character. Use 信頼する for trusting people or systems to perform well.
I believe his words.
I trust his ability.
English uses 'believe in', but Japanese uses the particle を with the object of belief. Do not try to translate 'in' literally as に or の中で.
I believe in this treatment method.