joining two 190x35mm to make one 190x70mm
What you have sounds very much like what we Americans would call a 2" x 8" (nominal size, actual size: 1.5" x 7.5" - yeah, we're weird that way...).

What you're proposing is making a 4" x 8" (70x190mm) out of it by nailing the two pieces together. That's not only perfectly acceptable, it's very commonly done for use as a header over a door or window*.  Usually, one puts columns (across the short dimension) of 2 or 3 framing nails (16d, ~0.131", 3.3mm)  through the two boards every 6-8" (150-200mm) apart (along the long dimension). 

Yes, this is very doable under US code and is very acceptable - it is probably acceptable under your local codes as well. You'd have to check your local building codes to confirm and to see if they have any specific requirements for nailing/screwing patterns and fastener sizes.

*For use as a header in a standard wall thickness, we also have to include a piece of 1/2" (12mm) thick plywood to make the header the same thickness as a standard 2x4" wall stud so that the finished surfaces are the same distance apart. This may or may not impact your situation.