I guess, because you are looking for the toilet/restroom/bathroom in the same restaurant/flat, so particular one, not just any toilet. For sure, when you are looking for toilet you don't care who is owner of it, but my neigborhood will be surprised if my guests will start to use his toilet). I may be wrong, but hope that folks will figure me out.
I can definitely get behind that use. I wanted to be polite in English speaking company once and asked where the bathroom was - they had a separate toilet so I had to come back and ask where THAT was... Now I'd just rather ask for the specific thing I need even if I might sound less polite.
"Restroom" seems an accurate translation of "туалет" to me, so I see no reason why it shouldn't be accepted.
And there's certainly no need to be offended just because your suggested translation wasn't accepted. That does by no means necessarily mean that it's incorrect, often it simply hasn't been added yet. Some people don't seem to realize that a human being has to add the translation, it doesn't just happen by magic...
In reference to the first part of your responce: that's right ! it is exactly what i was thinking, attending to the second part; i didn't know that the system is the same as Chelsea Handler thought that Shazam works :) ... don't get angry, it's a joke! Maybe i over reacted ? ? perhaps, but you have to understand, this is not the first time it happens. Finally and after all, thanks for answering my comment, Grod
I answered with "Where is a toilet?" but it was wrong. I thought <<туалет>> was nominative, not accusative. How do I know which article to use?
"Туалет" is used both as the nominative and the accusative form (in this sentence it's in the nominative), but I don't know why you bring that up, as it's got nothing to do with the choice of article in the English translation.
To answer your question: It's all about context. Since we don't really have any context here, it could theoretically mean "Where is a toilet?", so I suppose it should have been accepted. But, honestly, have you ever said that in real life? Think of it like this: If a Russian not very proficient in English asked you "Where toilet?", how would you understand that?