I have the wordpress language in Spanish. And the wpforo only changes some text, not all of them. I have half the forum untranslated. But if I make changes in the plugin's text area, I do not reflect the changes in the wpforo and I still have those texts in English.
As you can see the translation is not 100%, only 42% is translated at the moment:
You should expect that it'll not all phrases are changed. You can help it translate or translate it for your own only front-end phrases using wpForo Phrase System. Navigate to Dashboard > Forums > Phrases, search for untranslated phrase, edit and insert the Spanish version.
Forum Menu, User Reputation Titles and some other dynamic content should be translated in according settings area. More info in doc: https://wpforo.com/docs/root/translation/how-to-translate/
Thank you very much babri.