Hi, this is my suggestion of translation. First of all, speaking of the personal pronouns, you know, when you want to speak natural Vietnamese, you need to know the other age (or you can guess) to address them like anh, em, chị, etc instead of using "tôi". So I suppose you are "anh" and the other is "em" which means the other is younger than you.
How long are you living here? => Anh ở đây bao lâu rồi?
* I've just arrived. => Anh mới tới thôi.
* I am living here for almost a week already. => Anh ở đây được gần 1 tuần rồi.
Where in Vietnam are you from? => Em ở đâu ở Việt Nam?
* I am from Ho Chi Minh City. => Em ở Hồ Chí Minh.
Can I try it? [talking about food or drink] => Anh ăn thử cái này được không?
* Yes, go ahead. => Được, anh cứ ăn đi.
That way would be more natural. If you have any question, please feel free to ask. Enjoy Vietnamese language! :D