How to write "Happy Birthday" in Japanese?
For a birthday card to my best friend i would like to write this in Japanese, but i'm not sure how its called.

And i would like to have something like "i like you very much" or something like that. isn't it something like すきだよ　?

thank you!

Question

How to write "Happy Birthday" in Japanese?
For a birthday card to my best friend i would like to write this in Japanese, but i'm not sure how its called.

And i would like to have something like "i like you very much" or something like that. isn't it something like すきだよ　?

thank you!

Answer

In a polite formal way, it would be: 
Happy Birthday = お誕生日おめでとうございます。
I like you very much = あなたのことがとても好きです。

but since it's your best friend, it would be better to write it more frankly as: 
お誕生日おめでとう！君のことがとても好きだよ。

btw, "Happy Birthday" can also be written as "ハッピー・バースデイー" (the same pronunciation but in Japanese) because it's a common phrase.

Answer

Happy Birthday

Otanjoubi omedetou gozaimasu. (formal for elders/superiors)
お誕生日おめでとうございます。

Tanjoubi omedetou. (informal for friends/close familyl)
誕生日おめでとう。

Answer

Happy birthday! = 誕生日おめでとうございます！