How to Say "unsociable" in Spanish
The Spanish word for “unsociable” is “cerrado” — B1 level.
English → SpanishB1
adjectiveB1
not wanting to talk

Examples
Es una persona muy cerrada, le cuesta hacer nuevos amigos.
He is a very reserved person; it is hard for him to make new friends.
No la juzgues, solo es un poco cerrada al principio.
Don't judge her, she's just a little withdrawn at first.
Using 'Ser'
When describing personality, you use the verb 'ser' (to be) because being reserved is usually a permanent, defining trait of that person.
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