Saying "The restaurant is left" would make a native speaker think first, "The restaurant is remaining". Think if a fire happened on a city block, but a restaurant survived. You could then say, "The restaurant is left". If you wanted to give directions or imply location, you have to use a preposition like "on the" or "to the".
Yes. A lot of words borrowed from French keep their French pronunciation, although the spelling may change sometimes. For example: das Menü, das Büro, der Chef, die Chance, das Café, etc...
Here is a more complete list of German words borrowed from French if you're interested: http://german.about.com/library/blvoc_french01.htm
That works sometimes if there is something (like a street) that splits left from right. Then there is a left side and a right side. Sometimes you could be giving directions where there is not on obvious split and you are at the point at which you want them to look left, because that is where it will be.