How to translate plug-ins?


I have installed dozens of plugins and now it's time to translate them into my language. I have to use PoEdit for them, but before I start - can you teach me what to do on example of plugin "Blog Types"?

Should I edit these files:

or should I create new files, for example:

If so, from where will I be able to choose language. Same question about all translation-ready plugins.

Thank you