Dictionary in C2/C3 is "one-dimensional", it can only hold a simple list of keys and values.
If you open your file in Firefox or any other program that can view JSON files, you'll see that it has a complex structure - there are 4 or 5 nested levels. You can't simply import this into a single dictionary, you will get a mess. You will need to develop some sort of a "database" structure with multiple dictionaries/arrays and the way to link records between them. This is not an easy task.
There are a couple of plugins for C2 that allow to load and parse complex JSON files like this, but I don't know if any of those plugins were ported for C3.