If you mean the index, check your license that you have don't have the small version which only supports 2 languages. If you do, contact Episerver should and order at least the medium package.
Then index away...if you have Episerver content you should be able to create Dutch versions of pages and index those automatically (or using the scheduled job). Dutch is a supported language so should be no problem.
You can not add a language through any gui that I know of and as Daniel said, the smallest version comes with a two language limit.
with that said, you can index content in any language you want, the language selection when creating the index is for what language to support linguistics functions like stemming on.
If EPIFind is installed in Swedish and English, is it possible to install it Dutch as well? If Yes, how?
Thank you in advance.