Translations: Partially fix overtranslation in Serbian man pages

Translations: Partially fix overtranslation in Serbian man pages

Names of environment variables and some other strings must be present
in the original form. The translator couldn't be reached so I'm
changing some of the strings myself. In the "Robot mode" section,
occurrences in the middle of sentences weren't changed to reduce
the chance of grammar breakage, but I kept the translated strings in
parenthesis in the headings. It's not ideal, but now people shouldn't
need to look at the English man page to find the English strings.