"I have a good teacher."
Translation:Eu am un învățător bun.
Why "eu am un bun învățător" don't work (i am from Romania and "eu am un bun învățător" is correct
Yes, it is correct. But, unlike English, Romanian is very flexible regarding word order and this generates a big number of valid versions of the same sentence that is hard to manage. So most probably it happens that this one just wasn't added yet. You should report it so they can add it.