Why is Nước Cộng hòa Séc not accepted? Unbelievable.
My Vietnamese keyboard entry program (built into Mac computers), automatically puts the tone mark over the "o" in "hòa" even if I type it over the "a", and DuoLingo marks it wrong.
If you are using the built in Simple Telex keyboard on the Mac, try opening the Keyboard preferences for "Simple Telex" (in the input menu) and check "Use modern orthography". That will place the tone mark over the a.
My wife (who is vietnamesin but lives in czech republic) and her family use only nước Tiệp (but she knows also hoà séc)
Tiệp is the abbreviation of Tiệp Khắc (捷克), the Mandarin transliteration of Czech; officially it's the name of the former Czechoslovakia now.
I greatly prefer typing out Czech Republic in Vietnamese. Spelling that nation is just a nightmare for me in English for some reason.
Correct name is Czechia.