User login password not working for sudo
The trust chain can be broken in thousands of ways, so picking apart the specific failure might need some back and forth.

The good news - you can easily reset a password or make a new admin account so you can su to that account, then sudo or just enter the other user/password combination to unlock system preferences since any account can be used in addition to the logged in account to authenticate in macOS 

Here's the reset one, two official article and article here on just making a new admin account by re-running the out of box setup process:


https://support.apple.com/en-us/HT202860
Reset the password for a user when Snow Leopard is running as a VM?


Also, use locale specific keys or emoji password with caution. You might retain one admin account and password with a long but boring standard locale typable password.