"As you may have seen, I'm a Portuguese native speaker. However, what you don't know is that I'm very passionate about languages in general, which is why I decided to study Applied Languages at university. Among all the languages I've "come across" so far -- English, Spanish, French, Italian and Mandarin --, the truth is (American) English is undoubtedly and by far the one I love the most, which is why I want to be an English teacher in the future. Notwithstanding my good level of the language, one can always learn new things and improve certain aspects. Therefore, I appreciate all the help you can give me in improving my fluency and in achieving proficiency."
Does this sound natural? If so, how may I improve it and make it more advanced?

Thanks in advance

Question

"As you may have seen, I'm a Portuguese native speaker. However, what you don't know is that I'm very passionate about languages in general, which is why I decided to study Applied Languages at university. Among all the languages I've "come across" so far -- English, Spanish, French, Italian and Mandarin --, the truth is (American) English is undoubtedly and by far the one I love the most, which is why I want to be an English teacher in the future. Notwithstanding my good level of the language, one can always learn new things and improve certain aspects. Therefore, I appreciate all the help you can give me in improving my fluency and in achieving proficiency." 
Does this sound natural? If so, how may I improve it and make it more advanced?

Thanks in advance

ot_monforte · Answer

hello :)
two mistakes (they don't affect your message though):
- I appreciate all the help you can give me TO IMPROVE my fluency and TO ACHIEVE proficiency.
- If so, how CAN I improve it...

regardless of that, your English is excellent.
I would just be cautious. you are committing a mistake that every single person (this includes me) has already committed. at heart, this is a big mistake, but you can correct it as time passes by:
you're mixing discourses. that is, you make use of formal & academic language and informal & basic language in the same speech.
Informal & Basic Language:
- abbreviations (don't, I'm, I've...). this is informal.
- simple vocabulary (~B1/B2 or less words. this includes verbs, adjectives, nouns, adverbs, conjunctions, prepositions, etc.) 
- simple constructions (sentences like 'subject + verb + complement' or sentences only in present simple, past simple, etc.)
Formal & Academic Language:
- no abbreviations (do not, I am, I have...).
- wide range of vocabulary (~B1/B2 above words.)
- well made constructions (conditionals, inversions, fixed expressions to mean something in specific, etc.)
- complex ideas running in the background (this talks about what you're saying. are your arguments simple or complex?)
- cohesion (you should be able to transmit a message. thus, link sentences.)
- consistency (sometimes you choose to use A instead of B. simply by choice. use A throughout your text)

this may look like a guide to an essay, but it works almost all the same.
notice the difference, instead of 'simple vocabulary' (simple and basic), I could have said 'unvaried lexical range'.
in your text, you use abbreviations (informal) and the preposition 'notwithstanding' (academic), mixing up two different worlds. this makes the reader think you have just found out the word 'notwithstanding' and wants to use it wherever it is, not really caring about your text.

you got my point?

ot_monforte · Answer

@nunoaraujo19 yes, good job!

SierraRem · Answer

Sounds natural to me, nice job! Your passion for English has paid off