It seems that all locales are affected. For example, no matter which locale you switch to from https://mozillians.org/en-US/about, half of the page remains in English.
Besnik, thanks for pointing this out. Complete localization is a challenge for many Mozilla sites, and it's very difficult for us to have locales completely localized. Because the strings change frequently, I don't think we should commit to having zero string displayed. The good news is that we will make this better! Bug 845449 is about turning incomplete localizations into contribution opportunities so we'll have better coverage. Thanks for filing this bug and I encourage you to follow bug 845449 to see how we improve our localization coverage for the site :)
Thank you Besnik, we appreciate that you took the time to file this bug. QA verified wontfix