I’m currently subtitling the actors’ commentary of Shaun of the Dead, the first romzom (romantic comedy with zombies) ever. It’s a very funny film that I recommend, especially to zombie film fans like me who also like a good spoof. I came across "two-way mirror" and hesitated; was it "glace sans tain" or "glace sans teint"? I typed "glace sans teint" in Google: 428 hits. Quite conclusive, I thought. I typed in "glace sans tain": 562 hits. Not so conclusive anymore. I had a look at my dictionaries: it was "glace sans tain".
This is a great illustration of why I’m always very cautious when I use Google during my work. It can be brilliant to find information, facts, and latest developments in language that dictionaries haven’t had time to catch up on, but it can also lead to serious mistakes. All those billions of pages are, after all, written by fellow fallible fools, and it’s best to rely on trusted sources, like good old dictionaries.