Learn Finnish: Kaikki, mikä on täällä, on tietysti sinun. - Everything that is here is of course yours.

Usually, joka is the relative pronoun used for "which" or "that" when referring back to a specific noun. However, when referring back to a pronoun that represents an undefined whole or abstract concept, like kaikki (everything) or se (it), Finnish uses mikä instead. So, "everything that" is always kaikki, mikä.

Why is "here" translated as täällä instead of tässä?

Both words mean "here", but they cover different areas. Tässä refers to a very specific, exact spot, like right here in your hand. Täällä refers to a broader, more general area, like in this room or building. Since the sentence talks about everything in a general area being yours, täällä is the most natural choice.

Why is "yours" translated just as sinun?

In Finnish, the genitive (possessive) form sinun does double duty. It works as both the possessive word "your" before a noun, and as the independent pronoun "yours" at the end of a sentence. You don't need a special word for "yours" like we do in English; saying "is yours" is simply on sinun.

Why are there commas around mikä on täällä?

In Finnish punctuation, relative clauses (the extra information starting with words like joka or mikä) must always be separated from the main sentence by commas. This rule is much stricter than in English, which is why there are commas around "that is here" even though English leaves them out.