feat(translations): add translator app configuration

[chrismclarke]

Description

Adds support for a new Translator language configuration used to identify what text has/hasn't been marked for translation

Discussion

This should make it a lot easier to determine whether translations are missing because they have not been integrated in the code, or because the text is awaiting translation

Preview

Link to app preview if relevant https://picsa.app

Screenshots / Videos

Updated documentation https://docs.picsa.app/translations#preview-translations