Learn Swedish: Du behöver inte vara orolig. - You do not need to be worried.

Because rädd lacks a neuter singular form, you cannot use it to describe an ett word (saying ett rött barn means a red child, not a scared child). While you can sometimes use phrasing like rädd av sig, the most natural workaround for a temporary emotion is often just swapping in a related regular adjective like orolig (worried) or skrämd (frightened), which can comfortably take the neuter -t ending to become oroligt or skrämt.

Why use behöver inte instead of translating 'don't have to' with måste inte?

Both express a lack of obligation, but behöver inte is significantly more common and idiomatic in everyday Swedish. It is also a helpful way to avoid the classic learner trap: remembering that the English prohibition 'must not' translates to får inte, not måste inte. Relying on behöver inte keeps your meaning completely unambiguous.

If the subject were the plural ni instead of the singular du, how would this sentence change?

Because Swedish adjectives must agree in number with the noun or pronoun they describe, the adjective would take its plural -a suffix. The sentence would become Ni behöver inte vara oroliga.

How is the final letter in orolig treated in natural spoken Swedish?