How can I unlock my phone? I locked it using Android Device Manager, but it claims I entered a wrong password
I tested this on a Nexus 5 (v5.0.1) running UK English. I locked the device with Device Manager then, without unlocking it, I used Device Manager to lock it a second time. I then used the second password to unlock the device. So, you should be able to change the lock password using Device Manager - it seems that only the last lock password is required to unlock it.

You can use a one character password to lock the device. Perhaps give that a try?

Another thing you could try (assuming you are using the web page to lock your phone) is to use Device Manager on a different Android device to lock your phone. Perhaps there is something wrong with the translation between the characters in the language entered into the web page and those entered into your phone.

Hopefully someone else might have a better answer than this. :(