Learn Finnish: Myös sinä olet suomalainen.

Sinä means 'you' (singular), and olet is the matching form of the verb 'to be' (meaning 'are'). In Finnish, the verb ending changes to match the pronoun, so the -t at the end of olet always belongs to sinä.

Can I leave out the word sinä since the verb ending already tells us who is the subject?

While Finnish often lets you drop minä (I) and sinä (you), you need to keep sinä here. Placing myös (also) right before it specifically emphasizes the person. It literally means 'Also you are Finnish.' Without the pronoun, that emphasis has nothing to attach to!

Why isn't suomalainen capitalized?

In English, we always capitalize nationalities like 'Finnish'. In Finnish, nationalities, languages, and days of the week are written with lowercase letters. They are only capitalized if they happen to be the very first word of a sentence.

Does suomalainen mean 'Finnish' or 'a Finn'?

It means both! In Finnish, nationality words like suomalainen can be used as an adjective (Finnish) or a noun (a Finn). Because Finnish does not use words like 'a' or 'an', olet suomalainen translates perfectly to both 'you are Finnish' and 'you are a Finn'.