Bip39 tool - BIP32 Extended Private Key vs BIP32 Root Key
If you want to import a wallet, you should import a BIP32 extended private key. It is often derived from mnemonics.

What is the difference if I import the BIP32 Root Key or if I import the BIP32 Extended Private Key ?

The terminology is a bit confusing. The BIP32 derivation is done using a number, called the chaincode, over a private key (called the master private key). This private key has nothing special: it's just the starting point of the derivation.
The concatenation of a private key and the chaincode is called an extended key.
To import your wallet you need to import the master extended private key.
Regarding your question about BIP44, it is not a replacement to BIP32 just a set of recommendations of how to use it.
NB: you might be interested in the description of the key derivation process by the bitcoin.org documentation.