refactor: Deprecate language configuration and template methods

refactor: Deprecate language configuration and template methods

Configuration:

- languageCode      -> locale (either in root or per-language)
- languageName      -> label
- languageDirection -> direction

Methods:

- .Language.LanguageCode      -> .Language.Locale
- .Language.LanguageName      -> .Language.Label
- .Language.LanguageDirection -> .Language.Direction
- .Site.LanguageCode          -> .Site.Language.Locale

Example configuration:

[languages.en]
  direction = 'ltr'
  label     = 'English'
  locale    = 'en-US'
  weight    = 1

Closes #14269

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>