I saw that speech on French tv. They had a translator on tv + the translator on the court.
The tv translator gave quite an accurate translation of what Rafael Nadal was saying (praising Federer,...) at the same time of the speech (you could hear Rafael's voice + the voice of the tv translator at the same time). Once Nadal + the tv translator were done speaking, we were waiting for the on court translator to tell the crowd what Rafael was saying but he just translated a fraction of it and left out the praise for Federer.
It's my opinion that the crowd felt that the translator was leaving out a lot of things because Rafael was talking for quite a bit and the on court translation was simply too short to capture all that. So, in my viewpoint, they were whistling at the translator because they wanted to hear the whole speech.
About Guy Forget, I can't tell. I didn't watch the match itself on French tv.
I think that it's very possible that they wanted Federer to win the match (making history in France with the Roger slam thing) but Forget has given a lot of praise about Rafael Nadal in the past so unless he was lying then, I don't think he wanted Nadal to lose but he just was supporting Federer more.
But, this is just my interpretation.
Did anybody watch the most recent Davis Cup matches with France? Gasquet was playing against Tursunov and things weren't going well for Richard and when Richard showed signs of giving up, Forget was trying to motivate him by telling Richard that he wanted to see a Rafael Nadal attitude, a "fight for every point" attitude, a "never say die" attitude.
Forget has given enough praise towards Rafael Nadal in the past for me to doubt that he actually said that he was hoping that Nadal would lose but like I said, I didn't see the match on French tv.
About the arm thing: my guess is that Forget said that you don't need arms like that to play wonderful tennis. Young kids shouldn't rush to their local gym to try and get massive biceps. I don't think it was meant as an insult to Rafael Nadal.
However, there's an odd rivalry between France and Spain. Today, their soccer teams are playing against each other in the wordl cup and they were talking about that rivalry in the press here.