Are there any mistakes?

Besides, I attended related conferences which are presented were offered in the university.
Additionally, I started to the learn English as a second language and completed 4 levels of it. Spanish and French are among the languages which I am highly [daha doğal: very] interested in. However, I am [belki:] keen proned to learn nearly every language [He, he. 4 - 6 bin dil???]. Along During the learning process, I practised with native speakers in social language learning websites to improve my language skills. By this way [Daha doğal: This way veya By this means], I made lots of close friends from all over the world.

[In the light of your previous notebook entry, I suspect you mean 'have attended', 'have started', have practised', 'have made'. Both verb forms can be grammatical, so I cannot be sure. Tipik Türk sorunu!]

Are there any mistakes?

Besides, I attended related conferences which were offered in the university.

Additionally, I started to learn English as a second language and completed 4 levels of it. Spanish and French are among the languages which I am very interested in. However, I am keen to learn nearly every language. During the learning process, I practised with native speakers in social language learning websites to improve my language skills. This way, I made lots of close friends from all over the world.