A direct translation would be "Tämä tekee minut iloiseksi" ("this makes me happy"). You could also use the word "saa" (gets), instead of "tekee". However, the above is a relatively rare way to express happiness about something in Finnish. A more common way that would preserve the meaning somewhat would be e.g. "Se on hienoa minun mielestäni" ("I think it is great!"), but it wouldn't fit to all situations, because it doesn't emphasize happiness. However, without other context it is hard to give more suggestions. The first 2 ones will definitely be understood, though. Hope this helps :)