I'm hostile with the T'Rang and I don't remember what I did to be hostile. Is there a way to be friendly ?

Have you killed any of them? If you have loade a save befor you done that and dont kill am a gain!

You propably have good connections with Umpani, and T'rangs found out... too bad.

When you approach Z'ant, if you have a save before she went hostile, put whatever quest item is next for her (eg. flag) in your hand and click on her with it. Then she'll let you go on working for her. If you click lips on her, and some tattletale's been around, she'll go hostile.

It's too late, since I'm hostile with the T'rang I have 5 hours of play. I don't want to restart...

Besides of this, can I finish the game if i'm hostile with the T'Rang ?

Yeah you can complete the game without the T`Rang but it is not smart to do so! If you not will restart the save befor they got hostile then kill`em all! And make sure to colect all things Zant have!