Learn Croatian: Dvije pobjede i jedan poraz — dobar tjedan. - Two victories and one defeat

In Croatian, the number two changes based on the gender of the noun. You use dva for masculine and neuter nouns, but dvije for feminine nouns like pobjeda (victory).

Is pobjede in the plural here because there are two of them?

It looks like the nominative plural, but grammatically it is the genitive singular. In Croatian, the numbers 2, 3, and 4 require the following noun to be in the genitive singular case. For feminine nouns ending in -a, this form just happens to look exactly like the nominative plural.

Why does the word for "one" (jedan) match the noun's gender and case?

Unlike most larger numbers, the number one (jedan) behaves completely like an adjective. It must agree with the noun's gender, number, and case. Since poraz (defeat) is masculine and in the nominative case, we use the masculine nominative form jedan.

Why is it dobar tjedan instead of dobri tjedan?

Dobar is the indefinite form of the adjective, which translates best to "a good week". If you used the definite form dobri, it would mean "the good week". We use the indefinite form here because we are describing the week in a general, non-specific way.