I can confirm that the German release of Double Dragon is indeed REGION FREE. I was able to play it in my Region A blu-ray player last night no problem. Sure enough the back of the case says nothing about a specific region so color me surprised. If you're a fan of this 90s cheese classic like I am, I can whole-heartedly recommend this release. The only thing that sucks is there is a behind-the-scenes booklet included but it's all in German.
Also, Amazon.DE sent me two copies by mistake. I was charged for both and I really don't feel like going through the hassle of sending it back to Germany. So if anyone in the US doesn't want to import their copy, send me a PM and I'll sell it for what I paid for each ($19 shipped).