gen-inputs-and-outputs-list

When specified, the tool generates a JSON file containing the tool’s inputs and outputs, named gen_l10n_inputs_ and_outputs.json.This can be useful for keeping track of which files of the Flutter project were used when generating the latest set of localizations.  For example, the Flutter tool’s build system uses this file to keep track of when to call gen_l10n during hot reload.The value of this option is the directory where the JSON file is generated.  When null, the JSON file won’t be generated.

synthetic-package

Determines  whether the generated output files are generated as a synthetic package or at a specified directory in the Flutter project. This flag is true by default. When synthetic-package is set to false, it generates the localizations files in the directory specified by arb-dir by default. If output-dir is specified, files are generated there.

project-dir