If your developer is using a 301 Redirect then this is the best practice.
Google guideline (and I guess guideline from other search engines) is simple on this matter. When you are moving a URL and want to maintain its SEO value implement a 301 Redirect when the change is permanent.
You shouldn't redirect. You say "The system of my website determines the language of the browser", but you need to look into that more. It is not as reliable as you think. It is certainly not reliable enough to redirect.
There are two ways to determine the language of the user:
Use the Accept-Language header which usually comes with a language and ...