Testing: Václav äöüß
Ǎǎ Čč Ďď
Ěě Ǧǧ Ȟȟ
Ǐǐ ǰ Ǩǩ Ľľ
Ňň Ǒǒ Řř
Šš Ťť Ǔǔ
Ǚǚ Žž Ǯǯ
> I just pasted Václav here but it showed up as Vaclav and I had to go back in and manually replace the a with á.
Result: No problem here (Win7 & Firefox 50). Either by copy & paste your comment, as copy & paste from Wikipedia, as simply typing umlauts or diacritics.
Edit: Ah sorry, I overlooked that this topic is probably outdated. Not recognized the date.