I'm sorry but we don't support overriding package language files yet.

I'd be interested to know if you use that feature a lot. For what vendor?

It could be possible to implement it by loading several paths here: https://github.com/translation/laravel/blob/master/src/TranslationExtractor.php#L43-L71

And re-creating the translated files in the target paths here: https://github.com/translation/laravel/blob/master/src/TranslationSaver.php#L41-L55

The hard part is that we will need to create another internal key structure to be able to know in which vendor path a file should be written (like the existing subfolder/key1.key2... that is supported by Laravel for subdirectories in the locale).

vendor|subfolder/key1.key2... could be an idea.