confused after accepting PhD offer? Your experience or advice is very much appreciated! I have recently accepted a PhD offer. The subject is very close to what I was working on during my Master's years. I really worked hard back then and fortunately managed to publish high-quality papers.
I had several offers at the time and it was really difficult for me to choose between them since they were all good universities. I finally chose the university that I felt better about it and I was happy by my choice at that time. The factors that I liked about the place I chose were that: 

•   Their field is very close to what I have done during my Master's years and therefore I can easily proceed during my PhD.

•   The supervisor is a well-known person with a good resume and lots of connections in academia.

•   The chemistry seemed right and the supervisor seemed supportive and was very eager to have me as a PhD student.

The problem is, after some time passed, I started to develop lots of negative thoughts and now, some issues that were not important to me back then, are freaking me out right now.

I am thinking I decided too quickly and I should have applied to some better universities that I didn’t consider at that time.

First of all, The PhD offer that I have accepted is in a non-English speaking country. Although at first I was very eager and excited to learn a new language, it now freaks me out to live in a place where people don't speak my language.

Also, now I am thinking maybe my current field of research is not something worth pursuing. I was really passionate about this topic during my Master's years but now I am thinking maybe it is not a worthy topic and it will be too restricting when applying for a postdoc.
I don’t know what to do. I don’t want to decline my offer since I think it would really annoy the professor. And considering the fact that she has lots of connections in academia and that the academia is a very small world, I think it would be very bad for my reputation. But I just can't get rid of these negative thoughts.

I was wondering if anyone has been in this situation before and if this is common between students.

I appreciate any advice on this situation. Your thoughts and experiences will be a great help to me. 
Thanks a lot in advance. 

UPDATE:
Hi every one. Thanks for all the answers. It has been 6 months from when I posted this and I just wanted to share my experience, I hope it might help someone. 
I talked to the professor and asked for some extra time to decide. I was really lucky since the professor understood my situation and didn't pressure me. I ended up finding a much better offer and accepted the new one and I am totally happy about it.
Here is my advice to help others not to make the same mistake:
Never ever accept a PhD offer too quickly. Even if it sounds very good. Take as much time as you can and consider every option you have. Do talk to your classmates and previous professors. Their opinions might be very helpful to you when choosing an offer.
Hope that helps :)
Some doubts are pretty natural. While the bird in the hand may be worth two in the bush, those others look pretty sweet from a distance. I don't think any of the issues you raise should cause you to really want to switch except, possibly, the language issue. However, you should note that academics nearly everywhere are English speakers even if imperfectly. If the other country is, for example, in Western Europe, you will find that nearly every working age adult (and all kids) speak English very well. The issue will be in group situations in which they might prefer their native language over English. Then it would depend on their willingness to accommodate. If you are in a field in which large groups of people much interact it might be an issue. For daily life you can get along pretty well nearly everywhere. 

I've not been in your situation but have colleagues all over the world and language has seldom been an issue.

For everything else, I'd just suggest you relax.