I think your approach has to be different.
First, do not drop in any non English leads to your nurture until you are ready to send them. The leads will still be there.
Option 1: Segmentations
For this one, you will need to setup a Language Segmentation, which you need anyway.
Then update each email with the local content for each Segment as it comes out. Add the German leads to the Nurture once the emails are updated.
Option 2: One Nurture Program per Language
This might be a bit easier to manage given your setup. Just drop people by language into the appropriate program and don't turn it on until you are ready with content. If you want to send people English until German is ready, then just pull those German leads out of the English program when you are ready....keeping in mind you should start them with a different set of content (Stream 1: Normal; Stream 2: people who already were in English).