I posted this two days ago, but somehow it didn't go through. These are mostly changes for better style and clarity:
The reason I have decided to apply for admission to the English language course offered by the Perth College is because it is a good opportunity for me to master my English and to become more familiar with the Celtic culture and customs that I happen to find enormously interesting. I am a second year student of apllied linguistics in B., Poland. I have been a very hardworking and dedicated person, and I am also quite interested in movies and politics. As far as my work experience is concerned, I worked a translator during the annual music festival in B. in 2006, and, prior to this, I worked as a volounteer with mentally challenged children.
A few comments on changes I made:
"incredible chance" is a bit too strong. Sounds like you are jumping up and down
"good opportunity" is the right expression, so I just used it for both clauses.
"have proven" is not good to use when talking about yourself. It's ok when speaking about someone else or about a situation.
"held the job of" sounds like you were a temporary substitute worker for someone else, like you were holding someone's job while they were on vacation. "worked" is the best simple wording for jobs.
Best of luck to you. I've read a lot of good ESL articles from people in Australia, so I think it will probably be a good place for you.
BTW, I just finished my ESL certificate two days ago. I may end up teaching English in Ukraine if everything goes well.