It's a phrase, use "Search in Phrases" to search for "Home" (and maybe select the Exact Match radio button). If you're talking about the "Home-Forum-Blog-What's New" bar, then the phrase is called "site". You can edit that phrase and enter a translation to change the text.
Well, you could find where the phrase is used in the template and change it there (search for {vb:rawphrase site}), but that doesn't actually seem easier to me.