Move the configuration related to `Translations` that was previously stored in `Client` to a new `TranslationsConfig` object.
This makes things more explicit and consistent with the other focussed configuration objects.

BREAKING CHANGES: All elements that were in `Client` to manage the configuration of `Translations` have moved to `TranslationsConfig`:
  - `Client.defaultLanguage` to `TranslationsConfig.getDefaultLanguage`
  - `Client.setDefaultLanguage` to `TranslationsConfig.setDefaultLanguage`
  - `Client.language` to `TranslationsConfig.getLanguage`
  - `Client.setLanguage` to `TranslationsConfig.setLanguage`
  - `Client.languages` to `TranslationsConfig.getLanguages`
  - `Client.setLanguages` to `TranslationsConfig.setLanguages`