[9.x] Add method to extend localeArray generation

src/Illuminate/Translation/Translator.php

@@ -49,6 +49,13 @@ class Translator extends NamespacedItemResolver implements TranslatorContract
      */
     protected $selector;
 
+    /**
+     * The callable that should be invoked to determine applicable locales.
+     *
+     * @var callable
+     */
+    protected $determineLocalesUsing;
+
     /**
      * Create a new translator instance.
      *
@@ -325,7 +332,20 @@ public function parseKey($key)
      */
     protected function localeArray($locale)
     {
-        return array_filter([$locale ?: $this->locale, $this->fallback]);
+        $locales = array_filter([$locale ?: $this->locale, $this->fallback]);
+
+        return call_user_func($this->determineLocalesUsing ?: fn () => $locales, $locales);
+    }
+
+    /**
+     * Specify a callback that should be invoked to determined the applicable locale array.
+     *
+     * @param  callable  $callback
+     * @return void
+     */
+    public function determineLocalesUsing($callback)
+    {
+        $this->determineLocalesUsing = $callback;
     }
 
     /**

tests/Translation/TranslationTranslatorTest.php

@@ -221,6 +221,20 @@ public function testEmptyFallbacks()
         $this->assertSame('foo ', $t->get('foo :message', ['message' => null]));
     }
 
+    public function testDetermineLocalesUsingMethod()
+    {
+        $t = new Translator($this->getLoader(), 'en');
+        $t->determineLocalesUsing(function ($locales) {
+            $this->assertSame(['en'], $locales);
+
+            return ['en', 'lz'];
+        });
+        $t->getLoader()->shouldReceive('load')->once()->with('en', '*', '*')->andReturn([]);
+        $t->getLoader()->shouldReceive('load')->once()->with('en', 'foo', '*')->andReturn([]);
+        $t->getLoader()->shouldReceive('load')->once()->with('lz', 'foo', '*')->andReturn([]);
+        $this->assertSame('foo', $t->get('foo'));
+    }
+
     protected function getLoader()
     {
         return m::mock(Loader::class);