It will apply to that directory only – not sure if it would get crawled there. It would be best to implement in ur root folder and disallow any sub-directories you don’t want to be crawled. It’s all up to the crawlers to respect your directives then.
Ideally you should have it in the root file but if you have to place it in the sub-directory, then this is what we would recommend.

1. Specify the path in Google Webmasters

2. 301 Redirect the conventional path – domain.com/robots.txt to the new path.
If you have a multi-language website you should put every robots.txt in the first directory for every language sections of the website and not in the different sub-directory.