Querying

Product::whereSlug('red-chair')->first();                   // default column
Product::whereSlug('rc-01', column: 'handle')->first();
Topic::whereSlug('investovanie', locale: 'sk')->first();     // exact locale
Topic::whereSlug('investing')->first();                     // chain: current → fallback → supported
Topic::whereSlugIn(['a', 'b'])->get();
Topic::whereSlugInAnyLocale('investing')->first();          // current, fallback, supported, listed
Topic::whereSlug('gift')->orderBySlugPreference('gift')->first();
Product::findBySlug('red-chair');                            // ?Product (adds the preference order)
Product::findBySlugOrFail('red-chair');                      // ModelNotFoundException → 404

• whereSlug($slug, column:, locale:) — an explicit locale is exact; null follows the definition’s chain: current, then fallback, then (for Any) every supported locale and any listed in locales().
• whereSlugIn() takes a list, whereSlugInAnyLocale() ignores the chain and searches every resolvable locale (current, fallback, supported, listed), orderBySlugPreference() ranks the current locale first, then the fallback.
• findBySlug() returns the model or null and adds the preference order; findBySlugOrFail() throws ModelNotFoundException — a 404 in a controller.
• Passing a locale for a string column throws InvalidSlugDefinitionException (localeOptionOnStringColumn).

Scopes add predicates only — never an ORDER BY — so ->count(), ->paginate() and whereHas() sub-queries work on every engine; only the finders and route binding add the locale-preference order. Reads apply the model’s normal global scopes.

Packages with a swappable model should call the scopes through their seam (PostModel::query()->whereSlug(…)) rather than Post::findBySlug(…) — late static binding ignores the swap.