Nemoj tako glasno pričati u knjižnici.

Yes. Nemoj is the usual way to say don’t when giving a command to one person in Croatian.

In this sentence:

• Nemoj ... pričati = Don’t talk ...

Croatian commonly forms a negative command like this:

• nemoj + infinitive = don’t + verb

Examples:

• Nemoj kasniti. = Don’t be late.
• Nemoj vikati. = Don’t shout.

For plural or formal you, Croatian uses nemojte:

• Nemojte tako glasno pričati u knjižnici.

Because after nemoj, Croatian normally uses the infinitive.

So:

• nemoj pričati = don’t talk

not:

• nemoj pričaš ❌

You may also hear another negative command pattern:

• Ne pričaj! = Don’t talk!

So both are possible in Croatian:

• Nemoj pričati!
• Ne pričaj!

But in your sentence, the structure is:

• nemoj + infinitive
• nemoj tako glasno pričati

Here pričati means to talk or to speak in a general conversational sense.

It overlaps a lot with govoriti, and in many situations either can work. But there is often a slight difference:

• pričati = to talk, chat, tell, speak in a more conversational way
• govoriti = to speak, say, talk; often a bit broader or more neutral

So:

• Nemoj tako glasno pričati sounds very natural for Don’t talk so loudly
• Nemoj tako glasno govoriti is also possible and means nearly the same thing

Tako glasno means so loudly or that loudly.

• tako = so, that way
• glasno = loudly

The reason it is glasno and not glasan is that here Croatian needs an adverb, because it is describing how someone is talking.

Compare:

• glasan = loud (adjective, describes a noun)
• glasno = loudly (adverb, describes a verb)

Examples:

• glasan čovjek = a loud man
• glasno pričati = to talk loudly

So in your sentence, glasno modifies pričati.

Not always. Tako can mean several related things depending on context:

• so
• like that
• that way

In this sentence, tako glasno most naturally means:

• so loudly
• that loudly

So the full sense is:

• Don’t talk so loudly in the library. or
• Don’t talk that loudly in the library.

Knjižnici is in the locative case.

The preposition u can take different cases depending on meaning:

• u + locative = in/at a place, when there is no movement
• u + accusative = into a place, when there is movement toward it

Here the meaning is location, not movement:

• u knjižnici = in the library

Base form:

• knjižnica = library

Locative singular:

• u knjižnici

Compare:

• Ja sam u knjižnici. = I am in the library.
• Idem u knjižnicu. = I am going into/to the library.

Because knjižnica is a feminine noun ending in -a, and in the locative singular that ending usually changes to -i.

So:

• nominative: knjižnica
• locative: u knjižnici

This is a very common pattern for feminine nouns:

• škola → u školi
• soba → u sobi
• ulica → u ulici

So knjižnica → knjižnici follows a regular pattern.

It is addressed to one person, informally.

That is because of nemoj, which is the singular informal form.

If you were speaking to:

• more than one person, or
• one person formally

you would usually say:

• Nemojte tako glasno pričati u knjižnici.

So:

• nemoj = don’t ... (one person, informal)
• nemojte = don’t ... (plural or formal)

Yes, absolutely. That is also natural Croatian.

Compare:

• Nemoj tako glasno pričati u knjižnici.
• Ne pričaj tako glasno u knjižnici.

Both mean essentially the same thing:

• Don’t talk so loudly in the library.

The first uses:

• nemoj + infinitive

The second uses:

• ne + imperative

Both are common. Learners often meet nemoj + infinitive early because it is very straightforward and widely used.

Croatian word order is fairly flexible, though some orders sound more natural than others.

The neutral version is:

• Nemoj tako glasno pričati u knjižnici.

You could also hear:

• Nemoj pričati tako glasno u knjižnici.
• U knjižnici nemoj tako glasno pričati.

These alternatives change the emphasis slightly:

• Nemoj tako glasno pričati u knjižnici.
  neutral, natural

• U knjižnici nemoj tako glasno pričati.
  emphasizes in the library

So the exact order can shift, but the original sentence is a very natural standard version.

A rough pronunciation guide:

• pričati ≈ pree-cha-tee
• knjižnici ≈ knee-zhnee-tsee or knyee-zhnee-tsee

A few useful sound notes:

• č sounds like ch in church
• ž sounds like the s in measure
• nj is like ny in canyon

So:

• pričati → pri-ča-ti
• knjižnici → knji-žni-ci

You do not need perfect pitch accent to be understood; getting the consonants roughly right is much more important at first.

Sometimes yes, but knjižnica is the standard Croatian word for library.

• knjižnica = standard Croatian
• biblioteka = understood, but less standard in Croatian everyday usage

So in standard Croatian, this sentence is best as:

• Nemoj tako glasno pričati u knjižnici.

Yes, very common.

Croatian often uses:

• glasno = loudly
• tiho = quietly

with verbs like:

• pričati = talk
• govoriti = speak
• pjevati = sing

Examples:

• Priča glasno. = He/She talks loudly.
• Govorite tiho. = Speak quietly.
• Nemoj tako glasno pričati. = Don’t talk so loudly.

So this sentence sounds very natural and idiomatic.