Basic and Huttese

Why do Anakin and Watto speak only Huttese to each other if they can both speak and understand Basic when they're talking to Qui-Gonn and Padme?

 

The real question is, why does Watto suddenly break into basic when he recognizes grown-up Annie in Episode II?

 

I see plenty of Spanish speakers speak to each other in Spanish even though they both know English and speak English to everyone else.

 

They're bilingual. Is there a problem with that?

 

DJK edit: There's no need for that.

 

Huttese was both Anakin and Watto's primary language on Tatooine, so of course they used it. Watto used Huttese when doing business on Tatooine so they had been ended up using that between them because Anakin understood it too. He could have forced Anakin to learn Toydarian, but didn't perhaps see the point in it.
Anakin's first language is Basic (at least he uses that when talking to his mom), but he was property of Gardulla the Hutt from his third year. That's why his Huttese might be even better than his Basic, or if it isn't, then at least Watto's Huttese is better than Watto's Basic. He has an accent in his Basic, so I suppose he'd like to use Huttese while talking to people who know both languages.

But bigger question is, when two persons speak to each other, why the other one uses a different language than another? I understand when there's a wookiee or geonosian or other whose vocal chords cannot do Basic, but why does Palpatine's Rodian aide speak to him in Rodian, and Palpatine answers in Basic?

 

Very common. All the time you see people of Indian, Latino, or Asian origin speak in their native language to each other, but speak english when they are in the company of others ( Or at least America where the majority of people speak english..)