A lot of things.

app/Models/Language.php

@@ -3,8 +3,15 @@
 namespace App\Models;
 
 use Illuminate\Database\Eloquent\Model;
+use Illuminate\Database\Eloquent\Relations\BelongsToMany;
+use Illuminate\Database\Eloquent\Relations\HasMany;
 
 class Language extends Model
 {
     protected $fillable = [ 'name', 'slug' ];
+
+    public function entries(): BelongsToMany
+    {
+        return $this->belongsToMany(Entry::class, 'entry_languages');
+    }
 }