To make configurations without the admin GUI you can change the default parameters of the I18nModule directly in the webapp/WEB-INF/olat_config.xml file. The various options are well commented there.

From this config files the system reads the default configuration. Once an administrator uses the admin GUI to set the language parameters, the config is written into the olatdata user space. This user space configuration overwrites the default values. The configuration can be found in the file olatdata/system/configuration/org.olat.core.util.i18n.I18nModule.properties. This file can be deleted to restore the configuration to the default settings.