請幫我改這幾句英文

There were nothing wrong with your sentences, but I suggest you write as follow,
I believe they are more understandble.

Please let me know if you don't want to answer some of my questions

John said that he has been many countries.

Mary said that she won't go travelling next year.

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希望可以幫到你!

第一句我會改成,

If some of the questions I asked you makes you feel uncomfortable answering, you can always tell me.

John told me that he has traveled to many countries.

我見到既問題係禁多...不過我英文都唔係太好...希望幫到你啦...

第一句 : If I ask you some question what you don’t want to answer to me,you can tell me.
應改成I ask you some questions if you do not want to answer me, you can tell me.

第二句 : John told me that he has travelled many country.應改成John told me that he has traveled many countries.

最後 : Mary told me that she isn’t going to any country next year.應改成Mary told me that she will not go to any country next year.