It's the complete opposite. Taler wants to make decentralized transactions while keeping accountability and transparency. The idea of Taler is to have a system where buyers and sellers can have their data report to the authorities (at least what is needed for tax/compliance reasons) completely automatically.
You could do that with Monero as well. Ultimately, you would use a taxable system because you’re honest and want to pay taxes. So nothing about using Monero prevents the parties from reporting their transactions to tax authorities. Just as nothing prevents merchants from reporting their cash transactions.
The T in Taler stands for "taxable", and that's a big difference. Depending on where you (or your government) stand on the spectrum between maximum privacy and maximum accountability, Taler may be a better fit than Monero.
One is a chaumian cash system, the other is cryptocurrency with sender-obfuscation by ring-signatures.
The technical differences are too many for me to enumerate here. They are completely different technologies that make different efficiency-privacy-decentralization tradeoffs.
Functionally, Taler (and other forms of chaumian cash) are payment systems and not currencies. It requires a bank to implement it, in this sense it is less de-centralized, but likely much more efficient as there is no need for network consensus (because it depends on a central entity's blind signatures, etc. anyway). It has different (possibly better) privacy charichteristics than monero. They are both free and open source projects.