Search Tweets in a specific language


Hi everyone,
I’d want to resolve the following problem: I’m developing a web app and I need to research tweets for a keyword and in only a specific language.
I use this and that works but when I add the “lang” parameter don’t receive what I want. Results are the same with or without this padding. I noted that from this page the results are automatically corrected in my country language. So, are there any way to obtain the same result using
Thank you!