Added

• New language available: Arabic (MSA) ('ar'). Add language code constants and tests.

  Note: older library versions also support the new language, this update only
  adds new code constants.

  • #44 thanks to Ilmalte

Fixed

• Change document upload to use the path /v2/document instead of /v2/document/ (no trailing /).
  Both paths will continue to work in the v2 version of the API, but /v2/document is the intended one.
• Made DeepLException and subclasses, Usage and JsonFieldsStruct constructors public, to allow for easier mocking of the ITranslator interface.
  • #40 thanks to PascalVorwerkSaixon