The white stippling on the leaves is a clear sign of severe lacebug damage. The affected leaves cannot be changed back to their normal green color, but future infestations can be prevented. The dark spots on the leaves are a fungal infection of which there are many types.Leaves weakened by lacebugs would be more prone to secondary fungal attack.

There are a number of sprays and systemic drench type insecticides/fungicides that can be used. Best thing is to check with your extension service, state agriculture department, or good local nursery for their recommendation about what products to use and when to use them - timing of application is important.

Whitish specks on the upper surface of leaves and dark spots varnish-like on the bottom are symptoms of Rhododendron Lace Bugs, Stephanitis rhododendri, and Azalea Lace Bugs, Stephanitis pyrioides, small insects with transparent wings on under-surface of leaves. This insect hatches early in spring as the new foliage begins to mature and its numbers may build to damaging levels with successive generations. Lace bugs reach their peak in late summer and do their worst in sunny, exposed sites. Spiders are important predators of lace bugs and since they shy away from sunny, hot places, plant your azaleas where there is some shade. Insecticidal soap, horticultural oil, or a systemic insecticide may spare your azaleas the damage if applied in spring when the first hatchlings are noticed. Care must be taken to spray the lower surfaces of the leaves where the lace bugs live. Moving a plant to an area with more shade may alleviate the problem. Lace bugs are more prevalent on certain varieties. The following azalea cultivars have resistance to azalea lace bug: 'Dawn,' 'Pink Star,' 'Ereka,' 'Cavalier,' 'Pink Fancy,' 'Dram,' 'Seigei,' 'Macrantha,' 'Salmon Pink,' 'Elsie Lee,' 'Red Wing,' Sunglow' and 'Marilee.'

Here is a link that might be useful: How to care for azaleas