I would like to propose the following (updating my thoughts from a couple comments back):
cdk:name
This is the name of the CDK that was used to produce the canister’s Wasm module binary e.g. motoko, cdk-rs, azle, kybra, icpp.
cdk:languages
This is a list of strings indicating the source code languages that the CDK supports e.g. motoko, rust, typescript;javascript, python, c++
cdk:version
This is the version of the CDK that was used to produce the canister’s Wasm module binary e.g. 1.2.3, 0.16.2, 2.3