I have a problem with Inkscape and my plotter:
I can't print at the coordinates defined in the SVG file.
The image is printed resized.
How can I print the SVG file with the exact coordinates in pixels or milimeters?

I'm not sure I understand the problem. Perhaps you can attach a screenshot or an Inkscape svg file to illustrate this.

I have a A2 plotter 420mmx594mm but when I try to plot this file the plotter tries to plot outside the A2 area.

I have a A2 plotter 420mmx594mm but when I try plotting this file the plotter tries to plot outside the A2 area.

<?xml version="1.0" encoding="UTF-8"?>
<!-- color = rgb(000,000,000) -->
<svg width="420mm" height="297mm"
     viewBox="0 0 420 297"
     xmlns="http://www.w3.org/2000/svg">
<line x1="60" y1="46" x2="60.1" y2="46.1" stroke="black" stroke-width="0.25"  />
<line x1="358" y1="46" x2="358.1" y2="46.1" stroke="black" stroke-width="0.25"  />
<line x1="60" y1="248" x2="60.1" y2="248.1" stroke="black" stroke-width="0.25"  />
<line x1="358" y1="248" x2="358.1" y2="248.1" stroke="black" stroke-width="0.25"  />
</svg>

I'm getting the drawings enlarged by a factor of 2.54. Is it from Inkscape or plotter?

That svg looks nothing like inkscape's to me. Inkscape rather uses paths and adds way more style attributes and whatnot. Like a layer for one. 

Maybe it's optimised, but my best bet it's from somewhere else.

Inkscape is following the svg specs to the max so it's usually the plotter's fault not following along. 

They are usually set up at  72 dpi and assume user units as pixels.

However that 2.54 is very similar to the mm/inch ratio -25.4 mm=1 inch. Or this case, rather 2.54 cm=1 inch.

If you create a test file in inkscape svg format, we might have a better chance at guessing why the scaling occurs.

Though not generated by Inkscape, I see nothing wrong with your svg code.

I suspect that you're the latest in a long line of users to discover Inkscape's printing problems. It's usually windows users reporting this. I believe the linux version fares better. The customary workaround is to [File > Save a Copy...] and choose pdf as the file type. Try plotting the output from your favourite pdf viewer. 

Maybe check that the viewbox conventions are being followed: https://wiki.inkscape.org/wiki/index.php/Units_In_Inkscape#Inkscape_.26_Units

<?xml version="1.0" encoding="UTF-8"?>
<!-- Created with Inkscape (http://www.inkscape.org/) -->
<svg width="594mm" height="420mm" version="1.1" viewBox="0 0 2245 1587.4" xmlns="http://www.w3.org/2000/svg">
 <line x1="60" x2="60.1" y1="46" y2="46.1" stroke="#000" stroke-width=".25"/>
 <line x1="358" x2="358.1" y1="46" y2="46.1" stroke="#000" stroke-width=".25"/>
 <line x1="60" x2="60.1" y1="248" y2="248.1" stroke="#000" stroke-width=".25"/>
 <line x1="358" x2="358.1" y1="248" y2="248.1" stroke="#000" stroke-width=".25"/>
</svg>