How Many More To Go?
"save" and "save to next are basically the same thing. For the rally, only new translations (not changes to existing translations) count. Outdated translations count as untranslated.
You currently have 269 qualifying translations for MediaWiki core to Swahili, with 877 messages to MediaWiki core untranslated. The rules for the translation rally say you must translate MediaWiki core before working on other products. Given these two observations, you will still need to contribute 500-269=231 translations for MediaWiki core before you qualify for a share of the bounty. You have to keep translation MediaWiki core, until there are at most 877-231=646 untranslated messages left for MediaWiki core.
What if I do translations for a second language which I understand? Swahili has plateaued as far as my Swahili goes. It would need a language committee to come up with the technical remaining terms which are majorly computer-centric.
It would be awesome if you would be able to work towards getting that done for Swahili. The current situation is that we have an incomplete UI localisation, which isn't great for potential users of MediaWiki. We have very few contributors to Swahili, so I'm glad that you did contribute what you could. I'm going to make an exception and approve your claim. Please don't be a stranger, and keep coming back to contribute to Swahili localisation for translatewiki.net projects!