Writing the a letter to the a/my fictitious friend.

Task.
You have received a letter from your English-speaking pen friend (pen friend is correct, in North America so far as I know pen pal or penpal is more commonly used) Bill who writes:
"I don't think it will be a problem for me to choose a job in the future as I'm really interested in foreign languages, culteres cultures and countries and A little bit of a long sentence, as it is expressing two distinct ideas, consider splitting it into two sentences. I hope I'll work as a translator or teacher of foreign languages some day. Have you already decided on your career? What job are you going to choose? Why? What do your parents think about your choice?
I've lived in the USA my whole life but I'd really love to travel to other countries..."

My answer to Bill.
Dear Bill,
Thank you for your letter. I was really pleased to read it. According to your request, I'll tell you about my plans on future! "I'll tell you about my future plans" or "I'll tell you about my plans for the future"
Frankly, I have always been interested in animals! I used to spend hours playing with them when I was a child. Animals often need human's "often need people's help" perhaps? human's is singular, so this is stating that animals need the help of one human. "Animal's often need humans' help" would be referring to the collective help of many humans. Regardless, this is an awkward way to phrase it, and it may be a good idea to consider rewording. help, they are defenseless. I'm anxious to be a veterinarian when I've grown up. This sentence contains a verb tense shift. It's been a while since I've studied English grammar, so you may be more knowledgeable than me, but "I'm anxious" is present continous tense, and "when I've grown up" is ... not? I'm not entirely sure. Anxiety is typically associated with unease. So if what you're intending to express is that you're uneasy or nervous because you are not yet a veterinarian, then I believe the correct sentence would be "I'm anxious to be a veterinarian when I grow up". My parents accept my decision. Actually, as long as I'm happy they don't care what job I do.
As for travelling, I completely share your interest! Which countries are your favourite? The subject and object must agree, countries is plural and favorite is singular. This sentence could be "Which country is your favorite?" or "Which countries are your favorites?"  Who would accompany you? Do you prefer having a guide guided trip or not? Tell me more, please.
I have to go now.
Write soon.
Best wishes,
Olya

Waiting for your corrections :)

Task.
You have received a letter from your English-speaking pen friend Bill who writes:
"I don't think it will be a problem for me to choose job in the future as I'm really interested in foreign languages, culteres and countries and I hope I'll work as a translator or teacher of foreign languages some day. Have you already decided on your career? What job are you going to choose? Why? What do your parents think about your choice?
I've lived in the USA my whole life but I'd really love to travel to other countries..."

My answer to Bill.
Dear Bill,
Thank you for your letter. I was really pleased to read it. According to your request, I'll tell you about my plans on future!
Frankly, I have always been interested in animals! I used to spend hours playing with them when I was a child. Animals often need human's help, they are defenseless. I'm anxious to be a veterinarian when I've grown up. My parents accept my decision. Actually, as long as I'm happy they don't care what job I do.
As for travelling, I completely share your interest! Which countries are your favourite? Who would accompany you? Do you prefer having a guide trip or not? Tell me more, please.
I have to go now.
Write soon.
Best wishes,
Olya