My feeling is that it has never mattered to him, and to be honest there is nothing in the current direction the party is taking that compels him to learn Zulu or any other language besides Afrikaans. The DA has all but surrendered growth in KZN and will hope the IFP picks up the slack there, English is good enough for the Indian and other middle class communities, so whatever they get there will be fine.
Their focus is firstly on their own core voters and the part that keeps on going back to the Freedom Front, they want them back, hence the need that appeal largely to the Afrikaans community like the language thing and farm murders.
Zille's idea is that they keep what they have now, get 1 or 2 % back from the Freedom Front, hope for the best on everyone else, it will be another improvement on Maimane's 2019 result, with a low turnout it's possible, no one can accuse them of weakening the party. A risky strategy but at this moment both John and Zille are pretty much untouchable so it doesn't matter if it fails.