podebconf-display-po will give translators a rough idea on how their translation will look like, particularly the screens length (use this utility on a usual 80x25 terminal). But as cdebconf and debconf displays slightly differ, and as some scripts do heavy use of text substitution, one should not fully rely on this program. Running debian-installer is the only reliable solution to test your translation. (Note: this does not work for the po files from level 1 under sublevelX!)

Using podebconf-display-po is mandatory for testing debconf translations when they are mentioned to be tricky (such as shadow, popularity-contest and exim4 translations).