I'm a very new almost user of this really good script.
I have started with installing Osclass for local testing and for the beginning I bought the Beta theme for testing purposes on my local machine.
You know that no matter how many features we already have,we are always in a bad need for more customization.
So I have started learning the very basic things and reading the

How to extend fields article

and at one point , there is this:

Later, you should generate .mo and .po files for different languages and place them in folders inside the language folder.

Please don't get me wrong, but I'm going to kindly ask a stupid question:

How to generate  .po and  .mo files for a plugin?

You copy PO from English lang folder.
MO is generated on save.

Thank you for the prompt response.
My problem was to create the .po files, from plugin source code .
Let's say I would start creating My Very Ultra Special Brand New Plugin in order to add some new features to my site, for example.

Meanwhile, I have figured out that the good, free Poedit v3.1.1 has the option to generate the .po file from source code of let's say
My Very Ultra Special Brand New Plugin .

In Poedit:

File-> New->Set translation language-> Extract from source code.

After that, we can drag the project folder to the Base Path
and drag the excluded files to Excluded Path.
I will try this.
But I have to create My Very Ultra Special Brand New Plugin , first  

@oho
Just copy .PO from different plugin and update catalog properties, no need to re-invent wheel.