Identify this insect, found in Central Vietnam, with long antennae, black wings, and red body
This is a male scale insect, which are Hemipterans from the superfamily Coccoidea.

The one in your photo is probably from the Genus Drosicha. Here is the Wikipedia page for Drosicha corpulenta.

Here is an image, for comparison:



Here is another one, with black antennae, like yours:



There is no doubt that your specimen is a male because sexual dimorphism in Coccoidea is huge. Have a look at the females of Drosicha:



In conclusion, determining the exact species here is very difficult. However, we can be sure that the Genus of your insect is Drosicha.