So it's not actually code or algorithm driven -- it's a manual process based off of research others have done on letter frequency and then I pick a roughly even number of letters to get to comparable odds of a die roll.
For Czech I found a letter frequency chart here and using that I generated the following chart:
Please let me know if that works or if something is off frequency wise, but if it's good I'd be happy to churn out a Czech translation of the final doc.