I installed Guix on a new drive, so I tried the installer from the latest image. After reviewing the system config, the installer goes to a black screen where guix output is shown. Although I can see messages about substitutes being updated, and how much will be downloaded, all download lines are replaced with a seemingly random number of dots:
substitute: mise à jour des substituts depuis «…»... 100.0 %
4.5 Mo seront téléchargés.
Maybe this is related to the translation?