My Plan

Maybe, I can go to the Philippines next semester!I think can go to the Philippines next semester!

Don't use both maybe and I think.

(Just) Thinking about it makes me very happy!

"when" is correct, but the sentence could be shorter. You could also say something like "I can't wait!" or "I'm excited!"

I will improve my English communication skills and go to white sand beaches and clear turquoise waters !

You could use the words "communication skills" and "turquoise" but you do not need them. Choose clear or turquoise.

I really want to eat halo-halo.

keke

Halo-halo is ice flakes with tropical fruit, ice cream, and jelly/other toppings.

Now, in Korea, it's quite hot.

If I go, my brother would really like it because I won't be home.

But later, he will miss me.However, I know he will miss me later.

My plan

Maybe, I am thinking of maybe going to the Philippines next semester!

You could also say:
I am thinking of visiting the Phillipines next semester!

Why are you maybe thinking of going? If there is a reason you could say:

I am thinking of visitng the Phillipines next semester but it depends on....

I am very happy when I think about it!

This is fine but a little formal, you could also say:
"It makes me feel so happy/excited when I think about it!".

I will improve my English communication skills and go to white sandy beaches and with clear turquoise waters !

You could also say:
My trip will help improve my English and I will also visit sandy white beaches with clear turquoise waters!"

and I really want to eat try halo-halo

Halo-halo is ice flakes with tropical fruit and with icecream and jelly etc..

Now, inthe Korea, it's quite hot.

This is ok, but you could also say:
"At the moment it's quite hot in Korea".

I'd want to eat patbingsu, adzuki-bean riceflakes.>_<

It makes me want to eat patbingsu, which is made from adzuki-bean rice flakes >_<

If I decide to go, my brother will be happy because I won't be home!

but after a little time I am sure he will miss me!

I am looking forward to going.

This is fine if you have decided to go. At the start you mention that you are thinking about going. If you are still thinking about going, you may wish to write:
"I really hope I will get to go".

My Plan

"My Plan" it totally correct. Since it's a title, the first letters should be capitals, as you did. :)

Maybe, I think I can may be able to go to the Philippines next semester!

I am It makes me very happy when I think about it!

Maybe, I think I can might be able to go to the Philippines next semester!

I am very happy just when I thinking about it!

I will be able to improve my English communication skills and go to white sandy beaches and with clear turquoise water!

and I really want to eat try halo-halo.

Halo-halo is ice flakes topped with tropical fruits, ice-cream, jelly etc..

와! 맛있겠다!

Now, in the Korea, it's quite hot.

OR: It's quite hot in Korea these days. (More natural)

I'd I feel like want to eating patbingsu, adzuki-bean ice flakes.>_<

저도 한번 먹어 보고 싶어요! 정말 맛있는 것 같아요!

If I end up going, my brother will really like it because I won't be home but he'll miss me later.

but later, He will have missed me.