Cyrillics and InDesign

I have created af font also containing cyrillics and greeks. How do I make sure, that a customer can reach/use these letters in InDesign?? And see which languages are covered? Thanks!

What you can do from inside the font? Add the necessary glyphs, that is about it. Or what are you thinking about?

I have a customer who tells me, that there are no language choosable for Russia in Fontexplorer X Pro.
(I don’t use this software!), and there the Russian language is not displayed for the specific font?!

I do not know how FontExplorer calculates the languages. Probably checks for presence of key glyphs. Perhaps try your luck here: