According the Department of Justice (yeah, that's what they actually call themselves missing the Orwellian irony,) he's been charged, but the press release makes no mention of an arrest. I don't know if Vietnam has an extradition policy with the US or Germany, so it may be difficult for them to impose their injustice upon him. Let's hope.
As far as I know, Vietnam is a member of Interpol. So if Nguyễn is internationally wanted and eventually caught, he can be extradited at the request of any country, including Germany and the United States. However, trying to catch someone worldwide can be a really difficult task, even for Interpol. For example, Do Kwon was internationally wanted almost six months ago, but no one has caught him yet.