Questions & Answers about Er stelpan góð? Já, hún er góð.
Why is the word for "good" spelled góð here, instead of góður or gott?
In Icelandic, adjectives change their endings to match the gender of the noun they describe. Since stelpan (the girl) and the pronoun hún (she) are feminine, you must use the feminine form of the adjective, which is góð. For comparison, góður is masculine and gott is neuter.
Stelpan means "the girl". Since it has "the" attached, shouldn't the adjective use the weak declension?
That is a great observation! Normally, nouns with "the" attached take the weak form of an adjective. However, when an adjective comes after the verb "to be" (er) to describe the subject, it always uses the strong declension. This is true even if the subject is definite, which is why we use the strong form góð here.
How do we know stelpan means "the girl" and not just "a girl"?
Icelandic doesn't have a separate word for "the". Instead, the definite article is attached to the end of the noun. The base word for "girl" is stelpa. Adding the feminine "the" ending -in merges the vowels to create stelpan (the girl).
Why does the first sentence start with the verb Er?
Just like in English, Icelandic forms yes/no questions by moving the verb to the very front of the sentence. The standard statement is Stelpan er góð (The girl is good), and swapping the first two words makes it a question: Er stelpan góð?