how to add special characters for html encoding?

Can you please give me advice how I am able to add more special characters for html encoding ? Exactly I found out that it is not encoding following characters:
č Č ď Ď ľ Ľ ĺ Ĺ ň Ň ŕ Ŕ ř Ř ť Ť ž Ž
in html it is supposed to look like:
č Č ď Ď ľ Ľ ĺ Ĺ ň Ň ŕ Ŕ ř Ř ť Ť ž Ž

Thanks