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How do I know it CPU Monitoring is on or not?

You should read this.

I would like to translate this plugin to my language

No problem. The plugin ships with POT file so you can translate it to any language you like. Please get in touch with me so I can include your translation in the next update.

I activated it, where is the stuff?

There is an configuration menu under Options and another menu under Manage. The CPU Usage is under Manage.