Pilots available here?
If you are looking for how to find a speficic interface message here, you have a couple of options. The easiest is probably to just use Special:SearchTranslations and search for the misspelling to correct it.
The other option is that when you are on Wikipedia, you can add
?uselang=qqx to the URL. That will show the message keys in place of the translations. So where it says "Jumuia" in the menu on sw.wikipedia, it will now say "(portal)" instead. That means that you can find that specific message here on TranslateWiki at MediaWiki:Portal/sw. The same procedure can be used to find anything else you may want to correct, of course.