Recommend a localization framework for Briefcase

[yanokwa]

We get occasional requests for localization on Briefcase and this is an easy place for folks to contribute to Briefcase. Ideally, we'd use a lightweight framework that works with Transifex (our preferred localization platform) and IDEA (our preferred IDE)

Transifex formats

• https://docs.transifex.com/formats/java-properties
• https://docs.transifex.com/formats/java-xml-properties

[yanokwa]

@dcbriccetti @daveycrockett Do you have any recommendations?