Hi Mattias and welcome.
You are experiencing the usual frustrations of dealing with officials who are often completely clueless when confronted by someone who isn't just doing a fly-in package tour to their country.
What they tell you may have nothing to do with what you experience at the border, and the procedure when crossing a land border may be completely different than flying in with the bike (or worse yet, shipping it in by sea).
If you can afford to get the Carnet de Passage, I would do so, as you will have the smoothest process of all, no matter how you arrive. However, it is not REQUIRED anywhere in North, Central or South America at this time, despite what the embassies tell you.
If you don't have a carnet, each country determines its own requirements to allow you entry with a vehicle (and ensure you won't sell it in their country without paying duties).
In Central America, they stamp the driver's passport with the vehicle details, so that you cannot leave the country without the bike.
In North America, depending on your appearance (how poor or disreputable do you look), they may require evidence of funds, credit cards, and/or onward air ticket to satisfy them that you really are planning to leave the country. They may also require you to post a bond of some amount for the bike. It really depends a lot on the customs officials at the border you enter at.
In South America, any of the above might apply depending on the country. Ecuador and Brazil seem to be the worst for flying in, (though we do know people who have flown into Ecuador without a carnet. Also, see Ted Simon's experience on flying into Brazil last year. http://www.jupitalia.com/sep_txt_3.html
Chile and Argentina should be somewhat easier.
As for translating your documents, having them in English might be a good idea, as English is widely spoken in the Americas.
When you decide which location you will ship to, it would be worthwhile to contact the local HU Community to see if someone will meet you and accompany you through the process to assist with the translation. Ricardo Rocco has provided valuable assistance in this matter to travellers to Ecuador.
<font face="Verdana, Arial, Helvetica" size="2">At one embassy they told me to leglize the papers at all the spanish speaking countries consulate, for those countries that I will pass. </font>
I don't know what they mean by 'legalize', but that sounds like a waste of time to me.
Sorry not to be able to be more definitive. As a general rule, you should try to clean yourself up and get your hair cut before border crossings, as there is a general dislike of 'hippies' over here. Allow plenty of time and just be prepared for whatever hoops they want you to jump through. Consider it as part of the adventure!
Good luck and please keep in touch.
"It matters not what goal you seek
Its secret here reposes:
You've got to dig from week to week
To get Results or Roses."
'One world, two wheels'