For the content filter to populate it's fields, it needs a data source to fetch the entries from. The data source is a simple JSON file with the following structure:

{
    "Region 1": ["Language 1", "Language 2"],
    "Region 2": ["Language 1", "Language 3", "Language 7"]
}

The path of this JSON file needs to be specified in librarian's configuration file under the contentfilter.data_source_path key, e.g.:

[contentfilter]
data_source_path = /path/to/filter.json

contentfilter will read this data source on application startup, and populate the widgets in dashboard with the values found in it. When the configuration is saved through the UI, the chosen options will be stored in the setup file (librarian.json) and merged immediately into the global application configuration under the fsal.whitelist key in the appropriate form required by FSAL. The composed form of the chosen regions and languages is list of relative paths, e.g.: ["Region 1/Language 1", "Region 1/Language 2"], which is used by FSAL to whitelist file system entries.