Well then.

In many mainstream Pokemon games, the player character is usually silent except when answering simple yes or no questions. However, Red/Leaf and Gold/Lyra can be shown to speak when talking to the Copycat, as she will mimic the sentence that they have said previously.

...Or do you think that they're silent all the time?

Anyways, any theories as to why they don't talk, whether or not they do actually speak, etc. go here.

Well, a lot mainstream RPGs nowadays have the silent protagonist thing. Take SMRPG and Paper Mario series for example. Also, Dragon Quest VIII had a silent protagonist.

I think the point of it is that you're supposed to be the one speaking, if the character said whatever then it wouldn't really be you.

I think you talk, it just isn't popped up in a text bubble.

I've seen Fan made pokemon games where the main character talks. Trust me, it's a good thing that they don't. Having the character talk makes it hard to imprint yourself onto them, and it gets annoying if you don't like the character they picked.

If that's the case, then Gold, Samus, Red, Link, etc. are very foul-mouthed. (Watch my LPs.)

I think the best Nintendo franchises (Metroid, Zelda, Pokemon, etc.) do well without very much if any dialouge of the main character you're playing. It's appropriate for getting you into the character role.

Then other games like the Tales series use it quite well.

It's also very reminiscent of how older RPG's use to be (like on the NES) where it's kind of tradition now for several games to be voiceless. Other games started with voices or dialouge for characters (Final Fantasy, etc.) and have followed that path.