Use a 126 mm hub in a 130 mm frame.
 

Will I encounter any problem if I use a 126 mm hub in a 130 mm frame with two 2 mm "spacers" (this is not my native tongue), one on each side?

I'm gonna say, no, no problem....

A better way is to put both 2mm spacers on the left side. That way the cogs are the correct distance from the rear derailer instead of an extra 2mm away. If the wheel is already built, redishing is required.

put one on each side so the wheel stays centered and just adjust the derailer stop screw so it doesn't go all the way out.
The spacers should have some kind of ridge or teeth though, for gripping the frame. Observe how the dropouts and axelnuts do their thing on a normal bike without spacers to see what I meen.

Is this a steel frame bike? If a magnet will stick to it forget the spacers and just stick the hub on the bike, it has plenty of spring, anything else (except maybe ti) will be damaged, Al and carbon don't like to bend.
Wait, the axle it's self may be too long, the axle should not extend passed the dropouts or the quick release can't grip the frame(that will be obvious as you will be able to pull the wheel off the frame). If you are useing a solid bolt on axle it's good to go as they need to stick out (to screw the nuts on).

Works for me in several applications with steel frames.

Well, I was going to put the spacer between the locknut and the cone, there is already spacers there so one more or less shouldnt matter. I will see though if I put both on the same side or on opposite sides.
If there is no problem with the quick releases then I will skip spacers as suggested above and just clamp it together. Stupid of me not to have thought of that :)
And for you who wonder, it is a steel frame, an old Albuch Kotter, Columbus.