Use nl translations when no af available
Currently, when an Afrikaans translation is not available, users are forced to see English strings. Can we find another language that they are likely to know better than English, to use its translations?
According to http://www.let.rug.nl/gooskens/pdf/publ_JMMD_2007.pdf, nl (Dutch) is largely intelligible for Afrikaans speakers, though sometimes at first surprising. Would that be a good option for a fallback? I'm not sure since of course English is very used by Afrikaans speakers as well, while Dutch may be perceived as more distant.
Personally, I would like to see Dutch implemented as fail-back (instead of English). However, I don't know if the majority of Afrikaans users would agree with me on this. We'll need to somehow put it to a vote before deciding on the way forward.
While Dutch and Afrikaans are somewhat mutually intelligible, I strongly suspect that most Afrikaans readers would be pretty surprised by Dutch, and pretty unfazed with English. When it comes to computer/IT terms, Dutch and Afrikaans are pretty different. Between the two alternatives, English is very commonly used (and at times forced into our lives), so many people are familiar with it. Many are not even aware that technology can be anything but English. Half-translated user interfaces for software is fairly common, and the fallback is usually English. Windows and Firefox can only fall back to English, for example.
A typical adult in South Africa or Namibia has studied English for 12 years at school, and might have read one prescribe book in Dutch. Most people don't get much exposure, unfortunately.
Does mediawiki use the HTTP Accept-Lang header? That is somewhat of a solution for those that know to configure their browsers (very few people). Otherwise I think English is the best for now.