Sonic Charge's Bitspeek is your one stop VST for this kind of thing.

I love this plug. Also:

http://www.plogue.com/products/chipspeech/
http://blog.wavosaur.com/text-to-speech … audiounit/

You could use a combination of vocoder and bit crusher. Audacity is a free program with both plugins. The simplest work flow would be to take a vocal sample of speech as a wav. file., reverse it, then assign random notes to it through a vocoder plug in. Once you have a suitable robot esque inflection, apply the bitcrusher to give it a lo bit sound quality. You could then apply random splices manually and reorder the snippets of audio to give it an even more broken feel.

along this line, you could just feed your vocoder's filter bank with some chippy synth and modulate that w/ voice

For a animated series in voxel, I need to create two voices for two characters. There voices must look like a human voice (with intonation/inflexion) but not understandable, a bit like R2-D2. After what I'll match the dialogue sound with subtitles for the comprehension.
All in 8 bit of course.

So i search for a device, or softwar who can do that simply, possibly with a microphone (I think i don't need complicated features, cause i tried with some softwares but you know, i'm a noob in that stuff )

That's all, if you have an idea, thank you ^^ .