No, the usual way to say it is "guilty of arson."
Yes, if the defendant says and shows he/she is guilty.
it is not correct English, you rather say still
It is correct.
It would be more correct to say, someone who.
It is correct English to say decent skill but not decent ability
It's correct English but not very good English
It is correct English to say "He went off on a tangent".
no it is not correct to say you are not for sure instead you can say in proper English that you are not sure about something
No. In English we say "How old are you?"
Yes, it is correct to say out of compliance with. It means out of help with in English grammar.
no you should say "Did you get an A on the English exam?"
Correct is the same as it is in English. It means that it is free from error.