Hi might be this is a silly question, but as I am beginner learner of liferay so this is confusing me. In my project's liferay/tomcat/webapps/ROOT/WEB-INF/classes/content/ we have some Language-ext_*.properties file, but as I have searched in project there is no ext and even there is no hook corresponding to this properties file.
I also dont know how we can have our customized files inside ROOT directory.
My WEB-INF/classes directory contains only these files/directories (wildcarded for the legacy ones):
log4j.properties
logging.properties
META-INF
portal-legacy-*.properties
portal-developer.properties
So my guess is that someone manually put those files there. It's quite common to see that somebody did this. However, my recommendation is to not accept this mode of operation: It's tempting to fix something quickly with those files, without proper documentation. In case you'll have to restore the server any time in the future, you're never getting the same configuration/changes together again, so I'd purely demand to deploy all files within webapps/ROOT through plugins from everybody working with the system.
As you state in your comment, everything you want is to add russian translation, just do so with a hook: It's standard operation for this type of plugin and it's easy to maintain. Plus, it's best practice, hot deployable and quickly done