Learn Finnish: Hänen kielitaitonsa oli parempi kuin minun. - His language skill was better than mine.

In standard Finnish, third-person pronouns like hänen (his/her) require a 'double marking' for possession. You must use both the genitive pronoun (hänen) and the matching possessive suffix (-nsa or -nsä) on the noun. In casual spoken Finnish, people often drop the suffix, but written Finnish requires both.

How does the word parempi relate to the word for 'good'?

Parempi (better) is the irregular comparative form of hyvä (good). Just like in English where 'good' changes to 'better', Finnish uses a completely different stem for this word in its comparative and superlative (paras) forms.

Can minun just mean 'mine' all by itself?

Yes! Minun is the genitive form of minä (I) and usually means 'my'. However, when the context is clear, you can drop the noun it refers to. Here, kuin minun translates perfectly to 'than mine', saving you from having to repeat the whole phrase kuin minun kielitaitoni.

Why isn't the Translative case (-ksi) used here for the language?