I have a concept (let's call it A) that is being generated into a Ruby class using TextGen. I want to have the possibility to generate the same concept into other languages e.g Python. Could someone describe how to do it or some hint?
I recommend you use plaintextgen plugin (https://plugins.jetbrains.com/plugin/8444-com-dslfoundry-plaintextgen) for this. You can then just use reduction rules to generate the text. A tutorial for this can be found here: https://dslfoundry.com/plaintextgen-tutorial/
Using textgen aspect is also possible, but is much more involved for your use case, because it requires either that you have an existing MPS language for each text-based target language (Python, Ruby, C#, etc.) or that you implement a minimum version (at least containing the concepts and textgen aspects for the constructs you need in your generation result) of such a target language yourself.