https://en.wikipedia.org/wiki/Donaudampfschiffahrtselektrizit%C3%A4tenhauptbetriebswerkbauunterbeamtengesellschaft 79 letters, 9 letters longer than the Turkish word, huh?
https://en.wikipedia.org/wiki/Longest_word_in_English Of course. technical terms are ridiculously long and arguably not English.
Nope, first, one noun can only take one case at a time.
Second, the accusative case is only for specific direct objects. You will never ever ever see it in a phrase like this. The accusative case does not equal "the X." It just means that you have a specific direct object. :)
What is the "need" for Siz then, if bakkaldasınız can say the same thing as Siz bakkaldasınız. I assume there is a reason behind it.