I assume that it is made on the base of core (it sas that it was programmed by the "Bitcoin Wallet developers - but who am I to know...).
That assumption is wrong. Core does not have an Android app and never has had one. Your wallet is written by different developers and uses different technology. The wallet file is completely incompatible with Bitcoin Core.
However, I try to get hold of my private keys of this wallet. Only question: How?
Bitcoin Wallet for Android uses Bitcoinj. If you are comfortable using the command line and installing JDK and maven packages, then you can use the bitcoinj wallet-tool to extract the data from your wallet file. The wallet-tool is part of the Bitcoinj repository here:
https://github.com/bitcoinj/bitcoinjThanks.
Tried bitcoinj, but failed miserably
After executing this code:
./wallet-tool dump --dump-privkeys --wallet=[path to my wallet] > wallet.txt
I got an empty file wallet.txt and the following error:
Failed to load wallet '/path/to/my/Wallet: Could not parse input stream to protobuf
org.bitcoinj.wallet.UnreadableWalletException: Could not parse input stream to protobuf
at org.bitcoinj.wallet.WalletProtobufSerializer.readWallet(WalletProtobufSerializer.java:440)
at org.bitcoinj.tools.WalletTool.main(WalletTool.java:333)
Caused by: com.google.protobuf.InvalidProtocolBufferException: Protocol message tag had invalid wire type.
at com.google.protobuf.InvalidProtocolBufferException.invalidWireType(InvalidProtocolBufferException.java:99)
at com.google.protobuf.UnknownFieldSet$Builder.mergeFieldFrom(UnknownFieldSet.java:515)
at com.google.protobuf.GeneratedMessage.parseUnknownField(GeneratedMessage.java:205)
at org.bitcoinj.wallet.Protos$Wallet.<init>(Protos.java:14696)
at org.bitcoinj.wallet.Protos$Wallet.<init>(Protos.java:14653)
at org.bitcoinj.wallet.Protos$Wallet$1.parsePartialFrom(Protos.java:14859)
at org.bitcoinj.wallet.Protos$Wallet$1.parsePartialFrom(Protos.java:14854)
at com.google.protobuf.AbstractParser.parseFrom(AbstractParser.java:89)
at com.google.protobuf.AbstractParser.parseFrom(AbstractParser.java:95)
at com.google.protobuf.AbstractParser.parseFrom(AbstractParser.java:49)
at org.bitcoinj.wallet.Protos$Wallet.parseFrom(Protos.java:15710)
at org.bitcoinj.wallet.WalletProtobufSerializer.parseToProto(WalletProtobufSerializer.java:626)
at org.bitcoinj.wallet.WalletProtobufSerializer.readWallet(WalletProtobufSerializer.java:433)
... 1 more
Although I was able to extract the seed with wallet-decrypt, I'm wondering what went wrong here.