Are these all acceptable?

I'm asking the right orders/places of adverbs in the sentence such as "obviously", "definitely", "clearly" and etc.

1) English is obviously a far more useful language than Chinese.
2) English obviously is a far more useful language than Chinese.
3) Obviously, English is a far more useful language than Chinese.
4) English is a far more useful language than Chinese obviously.

Are the four sentences above all grammatically correct and acceptable?

yes, in my opinion, they are all acceptable.
It depends when you think of the word "obviously" when you say that sentence. But I think I prefer putting it in the front position in writing.

The mistakes: it's Spanish, not Chinese.

(1) and (3) seem to be the most acceptable, to me. (4) needs a comma before "obviously" to be acceptable.

^ I agree; the lack of comma after "Chinese" in the fourth one is the only mistake.

This really is pathetic, you're trying to cause a row, obviously.

I'd put a comma after English and after obviously in #2.

<<I'd put a comma after English and after obviously in #2. >>

If you put a comma after "English", you probably should put one before it, too.

<<If you put a comma after "English", you probably should put one before it, too. >>

Oops -- You should surround "obviously" with commas, not "English".

<<Oops -- You should surround "obviously" with commas, not "English". >>

That's what I said...One after English (or before obviously) and one after obviously.