I thought that "já" was emphasis only. So if I'm lazy and write only "jsem Kateřina", it's still technically correct. Sometimes Duolingo accepts omitted words and other times it doesn't. -.-
It is hard to understand what you are saying. Are you implying that "Jsem Kateřina" was not accepted? It should be and it is among the accepted forms.
Yes. They did not accept: "jsem Kateřina", they wanted: "já jsem Kateřina" Maybe because they want people to practice remembering "já jsem"? I don't know.
I repeat. "Jsem Kateřina." is in the list of accepted translations.
Which is strange as it did not allow me it. Maybe there was a glitch as I checked the spelling and it was fine :)
There also might have been some other typo. Or Duo does not have its day. That said though. In a short sentence like this when you are saying about yourself that you are this or that (katerina, teacher) you would actually use the personal pronoun in most cases. Not sure if it is because of the use of TO BE or because such sentences typically begin the conversation but to say just "jsem katerina" or "jsem ucitelka" is very unusual. Not wrong, just not typical.