OK, so I had a problem with this one too. I am so dedicated into creating this Dolphin site, that I decided to translate it to Polish, language which was not there from the start. So if you will do something similar, things won't be so easy. In the global language file there are some text strings for Forums, but they only cover those text strings, which are in the menu etc.
To make your translation you have to go to /modules/boonex/forum/integrations/base/langs directory, copy the PHP language file which you want to translate from to your hard drive (optional ; )), translate roughly 260 text strings, change the filename to fit your language, upload it back. Then you will see new option: compile language xxx as well.
If you don't see the changes, pruning cache is recommended.