Is it necessary to create a separate theme for adding a new language?

In docs I see that to add another language I should add translations to themes/mytheme/login/messages/messages_no.properties path.

Does this mean that I should create a new theme to add a language?

What if I only want to add another language/locale to the keycloak theme?

I’m using Keycloak Docker and after entering into the docker container, I don’t see the keycloak theme inside the /opt/keycloak/themes directory.

How can I add language to the keycloak theme, without adding a new theme?