De twintigste student is hier.

Because student is a de-word in Dutch, so its definite article is de.

In Dutch, singular nouns take either:

• de for common-gender nouns
• het for neuter nouns

So:

• de student
• het huis

Since student takes de, any phrase built around it also uses de:

• de student
• de twintigste student
• de aardige student

Twintigste is the ordinal form of twintig (twenty), so it means twentieth.

Dutch usually forms ordinals by adding -ste or -de to the cardinal number:

• een → eerste = first
• twee → tweede = second
• drie → derde = third
• vier → vierde = fourth
• twintig → twintigste = twentieth

So in this sentence, de twintigste student means the twentieth student.

In this case, twintigste is already the normal attributive form of the ordinal when it comes before a noun.

Dutch ordinals used before nouns usually appear in this form:

• de eerste dag
• het tweede boek
• de twintigste student

So you do not say de twintigst student. The -e is part of the correct form here.

A useful way to think about it: Dutch ordinals placed before nouns generally behave like adjectives and normally appear with this -e ending.

It is an ordinal number, but in sentences like this it behaves very much like an adjective because it comes before a noun and describes which one.

So in:

• de twintigste student

twintigste tells you which student. That is similar to how adjectives work in noun phrases.

You will often see ordinals in the same position as adjectives:

• de nieuwe student = the new student
• de twintigste student = the twentieth student

So grammatically, it is an ordinal, but in use it behaves adjective-like.

This is a normal Dutch main clause with standard word order:

• De twintigste student = subject
• is = finite verb
• hier = adverb

Dutch main clauses usually follow V2 word order, which means the finite verb comes in the second position.

Here, the subject comes first, so the verb comes next:

• De twintigste student is hier.

This is very similar to English:

• The twentieth student is here.

Yes, you can, but it changes the structure and emphasis.

• De twintigste student is hier.
  This is the neutral statement: the twentieth student is here.

• Hier is de twintigste student.
  This puts hier first, so the sentence sounds more like Here is the twentieth student or gives extra focus to here.

Because Dutch main clauses are V2, if hier comes first, the verb still has to stay in second position:

• Hier is de twintigste student.

You cannot keep the subject directly before the verb if another element is first:

• not: Hier de twintigste student is

Hier means here and tells you the location.

It is an adverb of place. In this sentence, it comes after the verb:

• De twintigste student is hier.

Dutch adverbs of place often appear later in the clause:

• Ik ben hier. = I am here.
• Zij woont daar. = She lives there.

So hier is simply giving location information.

A practical pronunciation is roughly:

• TWIN-tikh-stuh

A few useful points:

• tw sounds much like English tw
• the g in standard Dutch is a guttural sound, not an English g
• the ending -ste is pronounced something like stuh

A rough English-style approximation is helpful at first, but if you want more native-like pronunciation, pay special attention to the Dutch g/ch sound.

Often yes, but there is a nuance.

In Dutch, student often refers especially to a college/university student. For a school pupil, Dutch often uses:

• leerling = pupil/student at school

So depending on context:

• student can be a university student
• leerling can be a school student

That said, learners will very often see student translated simply as student.

No. In modern Dutch, student can be used generally, including for a person of unspecified gender.

If you want to specify female, you may also see:

• studente = female student

But in many contexts, student works as a general term.

So:

• de twintigste student does not automatically mean the twentieth male student

Because Dutch, like English, can directly place the ordinal before the noun:

• de twintigste student = the twentieth student

You do not need an extra construction. The ordinal simply modifies the noun directly.

Compare:

• de eerste dag = the first day
• de derde keer = the third time
• de twintigste student = the twentieth student

So this phrase is completely straightforward Dutch noun phrase structure:

• article + ordinal + noun

Yes, the article would change, but twintigste would stay the same.

For example:

• het twintigste boek is hier = the twentieth book is here

Compare:

• de twintigste student
• het twintigste boek

So the main change is the article:

• de for common-gender nouns
• het for neuter nouns

The ordinal before the noun still appears as twintigste.

No. In a normal Dutch sentence like this, you need the verb zijn (to be) in the finite form:

• De twintigste student is hier.

You cannot say:

• De twintigste student hier.

Dutch normally requires the verb in a complete main clause, just like English does:

• The twentieth student is here.

So is is necessary.