The date of the photo can be found roughly:

The series L (Serienwagen) were put into operation from 1956.

On September 24th, 1963 the tram route through the Eschersheimer Landstraße between Eschenheimer Tor and Dornbusch was closed due to the start of the underground construction.

The specialists can narrow it down even further using the advertising of the L-tram. The advertisement "Steinmetz-Brot" had L-tram 204 (from 04.1956 to 03.1960).

I have a stamped postcard from July 1959. It can be assumed that this was also the year, when the photo was taken.

Thank you for showing the postcard.