I would be grateful if you could correct my text :) (verb tenses need to agree)

Dear members of the selection committee,

I hereby apply for a place in the bachelor’s program in Interdisciplinary American Studies at University of ......
I found your program while looking for a suitable bachelor degree program so that and I was immediately interested in yours. 

My English had was not been as good as I desired in school, as unfortunately you can unfortunately see on my baccalaureate certification.  However, I have always been interested in the American language, culture and history, as well as, the English language, so I decided to go to America 2 years ago. (American is not a language, but a nationality)

So, I had been studying at the college for 11 months from 01/20/2012 to 10/19/2012.  It was a marvelous experience.  I met a lot of students of different ages, life stories, and also cultures who had different reasons for studying there.
(I think that is what you are trying to say.)

Thanks to the global language, English, we are connected with others cultures. Because of this opportunity, it was, or rather, it is possible for us to understand and to learn from each other.  Also, we are able to clear up the prejudice about other cultures and religions.

I could found out another interesting fact, that many English words are similar to German words and even some Arabic words such as, “mushrooms”.

I think I am a dedicated, motivated, independent, and focused person; and hopefully a future student.  I would like to learn from you and I hope that I may also contribute my own ideas and experience I made in my year abroad beyond the sea.

I am looking forward to hearing from you.

Yours faithfully,

Sign your name.

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Though I don't know German, I think that a lot of your mistakes in phrasing are due to using the type of phrasing in either German or the languages that you already know.  For example, I noticed that you confused the use of the verbs "to have" and "to be."  This is very understandable because they are used a little differently in English.  Some of your verb tenses were incorrect, but your overall thoughts were very good.  I think that if you work on your verb tenses and your phrasing that you will be on a great path to successfully mastering English.

Good luck.

Best i could do:

Dear members of the selection committee,

I hereby apply for a place in the bachelor’s program of Interdisciplinary American Studies at the University of ......

I found your program while looking for a suitable bachelor program and I was immediately interested.

My English needs improvement as you can see from my Baccalaureate certification but I am eager to learn.

I am interested in mastering the English language. I am also greatly intrigued by American culture and history which lead to my decision to come to America two years ago.

So I had been studying at the ......College ....... for 11 months from 01/20/2012 to 10/19/2012, it was a marvelous experience. I met many students of different ages and cultural backgrounds of which had various reasons for their choice of major. The life stories of the diverse community I encountered in America fascinated me.

Thanks to the global nature of the English language I feel a connection with other cultures. Because of this opportunity it was possible for me to clear up the prejudices about other cultures and religions.

I found out an interesting fact that many English words are similar to German words and some Arabic words such as “mushrooms”. I also learned that English has a number of loanwords from German such as kindergarten and dreck.  

I think I am a dedicated, motivated, independent, focused person and hopefully future student.

I would love to learn more from you! I hope that I may also contribute my own ideas and experience I made from my year abroad.

I am looking forward to hearing from you.

Yours faithfully,