Issue #3615447: Remove hardcoded language codes from routing and redirect logic

Sergey Drakrequested to merge
issue/myrest-3615447:3615447-i18n-remove-hardcoded into 1.0.x

The redirect subscriber compared against 'uk' and resolved aliases with 'ru', PathByAliasGetResource tested alias prefixes against uk/ru/en and fell back to 'en', and MyrestHelper carried an en/uk/ru month table that produced nothing at all for a fourth language.

Languages now come from LanguageManagerInterface. The two behaviours that cannot be derived from it are configuration: legacy_language_redirects maps a requested language to the one its unresolved aliases are retried in, and redirect_fallback_language is the last lookup. The shipped defaults reproduce the previous behaviour.

Co-Authored-By: Claude Opus 5 noreply@anthropic.com

Closes #3615447

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