Geturðu lánað mér reglustiku?

Because Icelandic very often joins a verb and the pronoun þú in questions.

So:

• getur þú → geturðu

This is a very common and natural written form, not just slang. You may also see the pronoun written separately, but Geturðu... is what learners will encounter all the time.

It is made from:

• getur = can / are able to
• -ðu = reduced form of þú = you

So Geturðu...? is basically Can you...?

This is the normal singular you form, used when speaking to one person.

After geta in this kind of sentence, Icelandic normally uses the supine form of the main verb.

So the verb is:

• lána = to lend
• lánað = supine form used after geta

That is why the sentence is:

• Geturðu lánað mér reglustiku?

This pattern is very common:

• Ég get lesið. = I can read.
• Geturðu hjálpað mér? = Can you help me?

The form often looks like a past participle, but here it is just the normal form used after geta.

Because mér is the dative form of ég (I / me), and the verb lána takes the person receiving the loan in the dative.

So:

• lána mér = lend to me

A useful mini-table is:

• ég = I
• mig = me (accusative)
• mér = me / to me (dative)
• mín = my / of me (genitive)

In this sentence, mér means to me.

Because it is the direct object here, and reglustika is a feminine noun that changes form in the accusative singular.

So:

• reglustika = nominative singular
• reglustiku = accusative singular

Since lána takes the thing being lent as a direct object, you get:

• lánað mér reglustiku = lend me a ruler

Icelandic does not have a separate indefinite article like English a/an.

So a bare singular noun can often mean:

• reglustika = a ruler

If you want the ruler, Icelandic usually adds the definite article to the end of the noun:

• reglustikan / reglustikuna = the ruler

So in your sentence, reglustiku naturally means a ruler.

This is standard Icelandic yes/no question word order: the finite verb comes first.

So the statement would be:

• Þú getur lánað mér reglustiku. = You can lend me a ruler.

But the question becomes:

• Geturðu lánað mér reglustiku? = Can you lend me a ruler?

That verb-first order is one of the most important patterns in Icelandic questions.

It is a normal, natural everyday request. It does not sound rude by itself.

However, like in English, you can make it softer if you want. For example:

• Geturðu lánað mér reglustiku, takk? = Can you lend me a ruler, please?
• Gætirðu lánað mér reglustiku? = Could you lend me a ruler?

So Geturðu... is fine and common, especially in ordinary conversation.

Because þú is singular.

So Geturðu... means you are speaking to one person.

If you were speaking to more than one person, you would use þið and a different verb form:

• Getið þið lánað mér reglustiku? = Can you all lend me a ruler?

This is an important distinction in Icelandic, since English usually uses the same you for both singular and plural.

They are two special Icelandic letters:

• þ is like th in thin
• ð is like th in this

So in this sentence:

• þú begins with the thin sound
• the ð in Geturðu has the voiced this sound

These two letters are very common in Icelandic, so it is worth getting used to them early.