"I will go to France after I go to Germany."
The で is can be omitted but that is not the standard. Not using the で is more a matter of style. you can also use に instead. Which of those three choices is more common depends on the surrounding words and style/tone. Someone postet a good explanation at another forum: http://yesjapan.com/YJ6/question/3503/what-is-the-difference-between-ato-ni-and-ato-de
It is because the theory that た form = past tense is actually not true. But it is a helpful way to remember which form to use when we begin.
The context of this sentence is, at some point of time in the future, when I have finished my trip to Germany, I will go to France. Using た form is in the same sense that I use the perfect form Have Finished here.