.properties is a file extension for files mainly used in Java related technologies to store the configurable parameters of an application. They can also be used for storing strings for Internationalization and localization; these are known as Property Resource Bundles.
You can either import and export .properties manually on the dashboard or you can automate your mozilla translation process with the Applanga Localization CLI.
empty_string_key = # Here is the description of the key with_description_key = This key has a description in some file-formats. with_line_break_key = This key has a line break\nin it. nested_key.level_one_a.level_two = A deeply nested key. nested_key.level_one_b = A nested key. plural_key[one] = Plural key one plural_key[other] = Plural key other plural_key[zero] = Plural key zero array_key = first entry array_key = second entry array_key = third entry simple_key = Most basic translation.