A missing -sl language now warns and continues, with or without --best-available. --require-subs counts a forced track only when selection keeps it, and a title with no track left is skipped instead of failing at mux.
BREAKING CHANGE: a missing -sl subtitle language no longer fails the run. Use --require-subs to fail on it.
A tag with a region (en-US, es-419) matches only that variant and reports a miss instead of taking another region. A bare tag takes the variant it means (pt -> pt-BR, es -> es-ES) and falls back to any variant only when that one is missing. `orig` prefers the title's own tag, `-sl orig` resolves, forced and SDH subtitles are picked from their own pools, and the track name no longer strips the region from the cached language.
BREAKING CHANGE: -l es-419 no longer selects es-ES, and language_priority, language_tags and muxing.default_language treat a regional tag as exact.
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