Translation:I want to go to Australia in the summer.
My assumption was that someone in the northern hemisphere(like Japan) wants to go during their summer, to Australia where it will be winter.
Interesting ambiguity here about whether the speaker means Japanese summer or Australian summer.
As an Australian currently dealing with spring weather, you do not want to be here for summer at this rate
We reached 46.6c last January (2019) in Adelaide. Don't think it got below 30c all week, even overnight.
that this letter is emphasised i guess, that's used in Spanish for example
There is no stress accent in Japanese but there is so called pitch accent. Google it to find out more.
Saying "the summer" rather than just "summer" should be optional. The former is more American English.
My best guess is that it's about how the -たい ending of the verb changes it to act like an adjective, and therefore, the journey isn't the emphasis. My guess is that with へ, the meaning would shift more towards the journey, and perhaps even emphasize the means of transportation? Seems reasonable to me that it would be like the difference between "I want to GO to Australia" and "I want to go to AUSTRALIA" Please correct me.
Of course it depends what you want to do but Aussie winter (June ,July ,August) temperatures are great ,say 12-24 C in Queensland. The summers are just as hot as Tokyo if not hotter in Sydney ,Melbourne and Adelaide. Even Hobart reached 40 C this summer(Jan)