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