Unngå unødvendige feil.

Unngå is the imperative form of the verb å unngå (to avoid).

So this sentence is giving a direct instruction:

• å unngå = to avoid
• unngå! = avoid!

In Norwegian, the imperative is often just the verb stem used on its own:

• Les! = Read!
• Skriv! = Write!
• Unngå unødvendige feil. = Avoid unnecessary mistakes.

Because it is describing a plural noun.

The noun here is feil, and in this sentence it means mistakes/errors in the plural. In Bokmål, adjectives usually take -e when they come before a plural noun:

• en unødvendig feil = an unnecessary mistake
• unødvendige feil = unnecessary mistakes

So:

• unødvendig = singular/common-gender form
• unødvendige = plural form

Here it is plural.

A tricky thing is that feil often has the same form in singular and plural:

• en feil = a mistake
• flere feil = several mistakes

So you understand the number from the context. In this sentence, unødvendige shows that feil must be plural.

Because Norwegian often leaves out the article when speaking generally.

Compare:

• Unngå unødvendige feil. = Avoid unnecessary mistakes.
• Unngå de unødvendige feilene. = Avoid the unnecessary mistakes / avoid those unnecessary mistakes.

The original sentence is talking about mistakes in general, not specific mistakes already known to the listener.

It literally means unnecessary.

It is built from:

• u- = un-/not
• nødvendig = necessary

So:

• nødvendig = necessary
• unødvendig = unnecessary

Yes. Feil is a very common Norwegian word and can cover both mistake and error, depending on context.

Examples:

• Jeg gjorde en feil. = I made a mistake.
• Det er en feil i programmet. = There is an error in the program.
• svare feil = answer incorrectly / answer wrong

So in Unngå unødvendige feil, English could be mistakes or errors, depending on the situation.

Yes, very natural. Norwegian often uses short, direct imperative sentences in instructions, advice, warnings, and headings.

For example:

• Hold døren lukket. = Keep the door closed.
• Vær forsiktig. = Be careful.
• Unngå unødvendige feil. = Avoid unnecessary mistakes.

This kind of sentence is especially common in:

• textbooks
• workplace instructions
• exam tips
• signs
• advice articles

It is fairly neutral. It sounds like standard written advice or instruction.

It is not especially rude, but it is also quite direct because it uses the imperative. If you want to sound softer, Norwegian often adds words like:

• Prøv å unngå unødvendige feil. = Try to avoid unnecessary mistakes.
• Du bør unngå unødvendige feil. = You should avoid unnecessary mistakes.

So the original sentence is normal and natural, especially in instructional contexts.

Å is a separate letter in Norwegian, not just an a with a mark on it. In unngå, it is part of the normal spelling of the verb.

A rough pronunciation guide:

• unngå sounds approximately like oon-goh with a rounded vowel at the end

A few helpful points:

• unng- can feel a little unusual for English speakers
• the å sounds somewhat like the vowel in British English thought for many speakers, though not exactly

You do not need to pronounce the word the way it would look in English spelling.

Yes, you could, but it is a bit more wordy.

• Unngå unødvendige feil. = shorter, cleaner, more natural in many instruction-style contexts
• Unngå å gjøre unødvendige feil. = Avoid making unnecessary mistakes

Both are understandable, but the shorter version is often preferred when the meaning is obvious.

Only if you mean specific mistakes.

Compare:

• Unngå unødvendige feil. = Avoid unnecessary mistakes.
  General statement.
• Unngå de unødvendige feilene. = Avoid the unnecessary mistakes.
  Specific mistakes already identified.

So feil is the better choice for a general piece of advice.