Translation:I know a great lawyer that can help you.
I prefer "I know an excellent lawyer who can help you.". I don´t like "great" or "that" in this context. "that" usually refers to things and "who" to people.
I agree with you about the "who" part, although there are many English speakers WHO get that wrong. The program definitely should not be marking it wrong though.
As for "ótimo," I suppose it could be translated either way (and if you hover over it above, it gives you both). But there is another word for "good" ("bom") and another word for "excellent" (excelente), so "ótimo" just falls nicely in between there. It also translates well to "great" as an exclamation upon hearing good news, as people who would say "Isso é ótimo!" would say "That's great!" in English more often than "That's excellent!" Perhaps it's overthinking it a bit, but I would just have to say that "ótimo" is the go-to word for anything better than just "bom" that doesn't need that emphatic "excelente" (after the noun).
English slangy-ness kind of makes these words equals...
No they are not. In English "Who" as rmacheshire says is correct for people. "That" is for objects.
Yep, I thought so too. It is one of my language pet peeves to see "that" when "who" should be used. And one day I was going to comment on that! Except I always research to back up my claims and turns out all the sources support "that" can be used even when "who" would work. :(
So while "who" works only with people, it is not the only one that works with people.
This is the closest I have found to support my previous beliefs:
I still very much prefer "who" with people and hope that someday it becomes the standard over that, but I will not be holding my breath. :(