'shirt' should be an option as well as t-shirt. Unless you wanted to be very specific, or you grew up saying, would you say t-shirt. Most people I know just say 'shirt'.
I fear that would be confusing. But we are considering using the unfortunate American English broad sense of "shirt".
I thought t-shirt was tričko not triko.
what do you think the difference is?
No idea. I just know that I learned tričko.
it didn't approve "a yellow t-shirt" though :(
"TO" žluté triko
Why didn't it approve "that" instead of "the"?
"I do not want that yellow t-shirt." is accepted.
But we have a report from the same time as your comment for "I do not want that yellow shirt." - which is "košile", not "triko/tričko". Although some people just say "shirt" instead of "t-shirt".
I wrote "I don't want that yellow t-shirt" and it wasn't accepted.
That's accepted. So you did not send a report?
I did send a report :)
In that case it's clear - the sentence you reported contained SHIRT, not T-SHIRT. ;) You may have done it by accident.