SG1 major plot hole Number 1
Why does every Alien in the universe speak english
Universal Translators
Because the Goa'uld and the Asgard ruled on Earth as gods? They would need to relate to their subjects over time. Not to mention the Atlanteans were on Earth for awhile. Considering those are three of the five races, one would think the Nox could have picked it up during their meeting alluded to back in season two I believe (when O'Neill first stuck his head in the ancients machine).
The Ori? Possibly because they read minds of their subjects? Not sure on that one.
Some of them don't - the Unas, for example. The Goa'uld use some variant of Ancient Egyptian among themselves, too.
Not just English, modern English, with an American accent. And almost all the aliens are humanoid. It is just pathetic.
The core cast is fine. The writing -- well, maybe Harlan Ellison still has a script or two in him.
Their ancestors learned it from Lord Vader.