Thank you for the pictures.  Your machine, although branded Triumph/Adler was actually made in Japan by Nakajima.  The ribbon which is fitted is the one that fits most Triumph/Adler machines, but actually the ribbon intended for Japanese portables (Brother or Silver-Reed) works much better.  As Fleetwing says, there should be grommets (eyelets)near each end of the ribbon that come up against the ribbon reverse forks and trip the reverse mechanism.  Your ribbon does not have these eyelets, and you will also find that the centre hole in the spool is too large.  No need to buy another ribbon for the time being.  Just tie a knot in the ribbon near each end, and the knot will do the same job as the eyelets/grommets !  Next time you buy a ribbon, get one intended for a Brother or Silver-Reed.

I found this -- the controls and internal layout look like your machine: http://site.xavier.edu/polt/typewriters/Nakajima.pdf

Try moving those ribbon gates and see whether the ribbon reverses. It should.