Við þurfum nítján stóla fyrir fundinn, en fundarherbergið hefur bara tuttugu.

Because the subject is við = we. The verb þurfa = to need changes form depending on the subject.

Present tense:

• ég þarf = I need
• þú þarft = you need
• hann/hún/það þarf = he/she/it needs
• við þurfum = we need
• þið þurfið = you all need
• þeir/þær/þau þurfa = they need

So Við þurfum means we need.

Because stóla is the accusative plural form, and here it is the direct object of þurfum.

• stólar = chairs as a subject, nominative plural
• stóla = chairs as an object, accusative plural

So:

• Stólar eru hér. = Chairs are here.
• Við þurfum stóla. = We need chairs.

It is accusative plural. The verb þurfa normally takes a direct object in the accusative, so nítján stóla means nineteen chairs in the accusative plural.

For learners, the main thing to remember is:

• þurfa eitthvað = to need something

So whatever is needed usually appears in the accusative.

Fundinn is the word fundur = meeting in the accusative singular definite form, meaning the meeting.

Breakdown:

• fundur = a meeting
• fund = meeting, accusative singular
• fundinn = the meeting, accusative singular definite

Here it comes after fyrir, and in this expression fyrir takes the accusative, so you get fyrir fundinn.

Literally, it is for the meeting.

• fyrir = for
• fundinn = the meeting

So nítján stóla fyrir fundinn is nineteen chairs for the meeting.

Because Icelandic usually puts the definite article onto the end of the noun instead of using a separate word like English the.

Examples from the sentence:

• fundinn = the meeting
• fundarherbergið = the meeting room

This is one of the most noticeable differences from English. Icelandic often does not have a separate standalone word for the in ordinary noun phrases.

It is a compound word:

• fundar- = meeting-
• herbergi = room
• -ð = the definite article

So fundarherbergið means the meeting room.

The first part, fundar-, comes from fundur and uses the genitive form as a linking element. This is very common in Icelandic compounds.

Because Icelandic very often uses the genitive form of a noun as the first element in a compound.

So:

• fundur = meeting
• fundar- = meeting's / meeting-

That gives:

• fundarherbergi = meeting room

This pattern is extremely common, so it is worth getting used to early.

Here bara means only or just.

So:

• hefur bara tuttugu = has only twenty

It is a very common everyday word in Icelandic, especially in speech and informal writing.

Because Icelandic can leave the noun out when it is already obvious from context.

The full idea is:

• fundarherbergið hefur bara tuttugu stóla = the meeting room only has twenty chairs

But since stóla has just been mentioned, Icelandic can naturally shorten it to:

• fundarherbergið hefur bara tuttugu = the meeting room only has twenty

English does this too sometimes, as in We need 19 chairs, but the room only has 20.

Because hafa = to have, and Icelandic uses it naturally for possession or what something contains.

So fundarherbergið hefur bara tuttugu literally means:

• the meeting room has only twenty

That sounds completely normal in Icelandic, just as in English.

Usually, in everyday use, nítján = nineteen and tuttugu = twenty are treated as forms that do not noticeably change here.

So in this sentence:

• nítján stóla = nineteen chairs
• bara tuttugu = only twenty

For a beginner, it is fine to learn these as stable number words. The noun around them is often the part that shows the important grammatical form.

Because the sentence means nineteen chairs, not the nineteen chairs.

So:

• stóla = chairs
• stólana = the chairs

Here the chairs are being mentioned as a quantity, not as a specific already-identified set, so no definite article is used.

It is fairly normal Icelandic main-clause word order.

The sentence has two main clauses:

• Við þurfum nítján stóla fyrir fundinn
• en fundarherbergið hefur bara tuttugu

After en = but, the second clause begins with the subject fundarherbergið, and the verb hefur comes right after it. That is exactly what you would expect in a normal main clause.

Yes:

• Við = we
• þurfum = need
• nítján = nineteen
• stóla = chairs
• fyrir = for
• fundinn = the meeting
• en = but
• fundarherbergið = the meeting room
• hefur = has
• bara = only / just
• tuttugu = twenty

So the structure is very close to English, even though the noun endings and the attached definite article work differently.