...wäre natürlich hübsch, ich weiß aber nicht, ob es da als Redensart gibt.

I hadn't heard it myself, but it's in both the Guardian (UK) and Time (US).

http://www.guardian.co.uk/freedom/Story/0,,13...
http://www.time.com/time/archive/preview/0,10...

'Tiger without fangs'? Fangs sound more dangerous than teeth.

Yeah, but the alliteration that comes with a toothless tiger ist so much more fun :-)

Und Google hat immerhin 67k Treffer dafür, darunter auch einige anerkannte Zeitungen / Zeitschriften (s.o. & Nature etc.). Man könnte sich jetzt fragen, ob die Redewendung nicht im Original sogar aus dem Englischen stammt.

This is, of course, not a literal translation, but the phrase was in quite common use a few decades ago with, naturally, essentially the same meaning. I think it came originally from a translation of the writings of Chairman Mao. While it has fallen out of use lately, I think it captures the idea, even though it tends to refer to political entities rather than to laws.

When talking about laws we just say ' the law has no teeth' in English