Now you have no other option left but do just that, as what you've stated means there are some. This is an Off-topic section of the forum, so you have the right to unleash yourself (and I would not mind)...
Not exactly grammatical errors, but allow me to try...
How would you know if English is your native language (is it?)? - I kind of take this to mean that you're asking him if he is sure that English is his native language. So, maybe a comma in there might help: "How would you know, if English is your native language?" though it may be more clear the other way around: "if English is your native language
, how would you know?".
I don't think it difficult (English grammar at least) - I'm not sure you can omit the implicit "is" in there: "I don't think it
is difficult (English grammar at least)"
neither do I find myself specifically capable at learning foreign languages - I don't know if "specifically" is the best word to use in this context; you're sort of specifying something indeed, but it kind of sounds weird to me. Also, did you mean "incapable" instead of "capable"? And "of" instead of "at"? That way, I think you're saying that you don't find yourself capable of learning foreign languages. "neither do I find myself specifically
incapable of learning foreign languages"
Anyway, that's all I got. I hope someone else can help out (and probably point out my own mistakes).