Create dynamic properties with automapper php?

I use automapper component (https://jane.readthedocs.io/en/latest/components/AutoMapper.html)

My source can have array properties with keys and values not known in advance. In the example below for example the title of a document in several languages ['fr' => 'Mon titre', 'en' => 'My title']; Is it possible to set dynamic properties to the target (target is an array) as
$target[title_fr] => Mon titre; $target[title_en] => My title;

I was wondering if we could write something like below (it doesn’t work of course) with this type of library:

 class SolrDocumentMapperConfiguration implements MapperConfigurationInterface
{
    public function getSource(): string
    {
        return Content::class;
    }

    public function getTarget(): string
    {
        return 'array';
    }
    /**
     * @param MapperMetadata $metadata
     */
    public function process(MapperGeneratorMetadataInterface $metadata): void
    {
        $metadata->forMember('rank', static fn (Content $content) => $content->getRank());
        $metadata->forMember('title_'.$keyLang, fn (Content $content) { 
                foreach ($content->getTitles() as $keyLang => $titleLang)
                return $titleLang;
             }
    }
}

Thanks in advance for any help.