这是不是一个缺点，这是一个机会！

1 This is not a disadvantage, this is an opportunity!
这是不是 釘子一个缺点，这是一个机会！

2 I think you should know that I have accomplished every single goal I set, learning Mandarin, will not be an exception.
我想你应该知道，我已经完成了每一 志向我所愿都己经完成了个进球我设置，学习普通话，也不是会例外。

3 I promise you: You will realize that no matter what happens I will win! / You will realize that no matter what happens I will become fluent in Mandarin!
我对向你承诺保证：你要知到会意识到，无论如何, 我一定会贏的! / 不管发生什么事情我会成功！/ 你会意识到，不管发生什么事情，我会成为讲流利的普通话 一定会 口出珠流！

这是不是一个缺点，这是一个机会！

1 This is not a disadvantage, this is an opportunity!
这是不是一个缺点，这是一个机会！

2 I think you should know that I have accomplished every single goal I set, learning Mandarin, will not be an exception.
我想你应该知道，我已经完成了每一个进球我设置（我设置的每一个目标），学习普通话，也不会例外。

3 I promise you: You will realize that no matter what happens I will win! / You will realize that no matter what happens I will become fluent in Mandarin!
我向你保证：你会意识到，不管发生什么事情我会成功！/ 你会意识到，不管发生什么事情，我将会成为讲一口流利的普通话！

这是不是劣势，这是个机会！

I am not sure about what's the proper Chinese translation for disadvantage here, but is it definitely not a “缺点”. “劣势” is a better translation IMO, since it has the connotation of being in a bad position and situation. 

2 I think you should know that I have accomplished every single goal I set, learning Mandarin, will not be an exception.
我想你应该知道，我已经完成了每一个进球我设置，学习普通话，也不会例外。

3 I promise you: You will realize that no matter what happens I will win! / You will realize that no matter what happens I will become fluent in Mandarin!
我向你保证：你会意识到，不管发生什么事情我会成功！/ 你会意识到，不管发生什么事情，我会成为讲流利的普通话！

这是不是一个缺点，这是一个机会！

1 This is not a disadvantage, this is an opportunity!
这是(should delete it)不是一个缺点，这是一个机会！ (but I often say 这不是一个缺点反而是一次机会）

2 I think you should know that I have accomplished every single goal I set, learning Mandarin, will not be an exception.
我想你应该知道，我已经完成了每一个进球我设置（我设置的每一个目标），（I often say当然也包括）学习普通话。也不会例外。

3 I promise you: You will realize that no matter what happens I will win! / You will realize that no matter what happens I will become fluent in Mandarin!
我向你保证：你会意识到，不管发生什么事情我会成功！/ 你会意识到，不管发生什么事情，我会成为讲流利的普通话！  I often say 我保证：不管发生什么，我都会成功。/你会知道无论（不管）发生什么，我最后都能说一口流利的普通话。

这是不是一个缺点，这是一个机会！

1 This is not a disadvantage, this is an opportunity!
这是不是一个缺点，这是一个机会！

2 I think you should know that I have accomplished every single goal I set, learning Mandarin, will not be an exception.
我想你应该知道，我已经完成了我设定的每一个目标进球我设置，学习普通话，也不会例外。

3 I promise you: You will realize that no matter what happens I will win! / You will realize that no matter what happens I will become fluent in Mandarin!
我向你保证：我要让你知道会意识到，不管发生什么事情我都会成功！/ 你会意识到，不管发生什么事情，我都将会拥有一口会成为讲流利的普通话！

很好,继续努力,加油!!