Never worry about that! I've been stomping all over it since I started playing Jake XD I usually try and remember to put the translation (or, y'know, what I hope I'm saying) into the mouseover text so that the actual Na'vi doesn't have to be 100% right, or if I am stuck or can't be bothered with translating, there's always [dialogue like this]
The Navilator seems pretty basic. It'll give you roughly what you're after but it doesn't get everything. I asked it for the Na'vi for "I am part of the People" (Na’viyä, oe lusu hapxi! - He said it to Lexa yesterday) and it gave me back "I part party" (Oe ma hapxi pongu). Then I asked for "I am not a sky person" (Oe kea tawtute ke lu - technically, 'I am no sky person') and got "I not sky person" (Oe ke taw tute). So yeah, it's a bit hit and miss.