The weaker the currency of Australia compared with China, the...

The weaker the currency of Australia compared with China, the more of the currency of Australia can be bought by China and - therefore - the cheaper the products of Australia are to Chinese.

True, in the context of A2, I perhaps shouldn't of mentioned converting earnings in China to New Zealand currency because your post implied all A2 sales are exports.

I hold shares in Bellamy's who do have foreign earnings, they have business units in several Asian countries, therefore earning foreign currency.

To clarify the Export/Import situation with respect to currency devaluation.
If Australia is importing raw materials from China to make the products to export, the cost of those imports will be greater to Australia and are likely to increase its manufacturing costs and the price of its exports or reduce the percentage of profit of those exports.

When the Australian dollar falls in value against the Renminbi the tin of A2 formula will appear cheaper in Renminbi terms to the importer. Market forces will determine the retail price.