adding i18n integrity check for valid YAML and valid content (PR #538)

  1. adding server.id.yml and server.sv.yml (with contents of the English locale), because they were completely missing
  2. adding another i18n sanity check for validness of YAML and for corrent root nodes

GitHub

You’ve signed the CLA, kubabrecka. Thank you! This pull request is ready for review.

Great stuff! :fish: