To change the default reader language, open the group options and select Publication Reader.
In the Display & Formatting tab you can select the language which is applied to all publications in the group.
You can also select a reader language on publication level. This setting will overwrite the default value set in the Publication Reader menu and will only apply to the selected publication.
You can find the publication settings under the options available on the right in the publication overview (•••).
Supported Reader languages: