confused after accepting PhD offer? Your experience or advice is very much appreciated!
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.