Við söfnuðum hundrað undirskriftum áður en húsfélagið samþykkti nýjar reglur um sameiginlega þvottahúsið.

Because söfnuðum is the past tense of safna for við = we.

• safna = to collect, gather
• ég safnaði = I collected
• við söfnuðum = we collected

So the ending -um tells you the subject is we in the past tense.

Unlike some languages, Icelandic usually keeps the subject pronoun.

So even though söfnuðum already shows first person plural, við is still normally present:

• Við söfnuðum = We collected

Leaving við out is not the normal neutral choice in a sentence like this.

Because safna takes the dative case.

The noun undirskrift = signature changes like this in the plural:

• nominative: undirskriftir
• accusative: undirskriftir
• dative: undirskriftum

Since the verb is safna + dative, you get:

• safna undirskriftum = to collect signatures

So hundrað undirskriftum means a hundred signatures in the dative because of the verb.

Hundrað is very often unchanged in form. The case marking is shown more clearly on the noun after it, not on hundrað itself.

So in:

• hundrað undirskriftum

the important visible case ending is on undirskriftum, which is dative plural.

Húsfélagið is a compound noun:

• hús = house, building
• félag = association, society, group

So húsfélag means something like the residents' association, building association, or condo association, depending on context.

The ending -ið is the definite article, so:

• húsfélag = a building/residents' association
• húsfélagið = the building/residents' association

Samþykkti is the past tense, third person singular form of samþykkja = to approve, accept, adopt.

Here the subject is húsfélagið, which is singular, so the verb must also be singular:

• húsfélagið samþykkti = the residents' association approved

Because the phrase is indefinite here: new rules, not the new rules.

• reglur = rules
• nýjar reglur = new rules
• nýju reglurnar = the new rules

Also, samþykkja takes a direct object, so reglur is in the accusative plural. For this noun, nominative and accusative plural happen to look the same: reglur.

The adjective nýjar is the strong feminine plural form, which is used with an indefinite noun.

This is about strong vs. weak adjective forms.

• nýjar reglur is indefinite, so the adjective uses a strong form.
• sameiginlega þvottahúsið is definite, so the adjective uses a weak form.

Compare:

• sameiginlegt þvottahús = a shared laundry room
• sameiginlega þvottahúsið = the shared laundry room

So sameiginlega is weak because the noun is definite.

Because um takes the accusative case.

• um = about, concerning

So:

• um þvottahúsið = about the laundry room

Here þvottahúsið is neuter singular definite. In neuter singular, nominative and accusative often look the same, so you do not see a different ending on the noun itself.

Áður en means before and introduces a subordinate clause.

So:

• áður en húsfélagið samþykkti nýjar reglur
  = before the residents' association approved new rules

It links the two actions in time:

1. we collected a hundred signatures
2. before the association approved the rules

Because after áður en, you have a subordinate clause. In subordinate clauses, Icelandic does not use the normal main-clause verb-second pattern in the same way.

So the more normal order here is:

• áður en húsfélagið samþykkti ...

with the subject húsfélagið before the verb samþykkti.

Yes. In Icelandic, the definite article is usually attached to the end of the noun.

So instead of a separate word like the, Icelandic often uses a suffix:

• húsfélag → húsfélagið = the residents' association
• þvottahús → þvottahúsið = the laundry room

That is one of the most noticeable differences from English.