Druids who want to cast spells while using wild shape need to take the "Natural Spell" feat, and they would need to take the "Wild Speech" feat in order to actually speak while using wild shape. The latter feat specifically calls out animal forms as forms where you can't speak without the feat.
Since wild shape uses the beast shape spells, the rules should work the same for a non-druid who casts one of those spells. Unfortunately, the feats mentioned are not applicable to non-druids, so a wizard, for instance, would be out of luck, unless they choose a form that can actually speak (ie; they have a language listed).
You cannot speak (and especially can't use Verbal components) in Beast Shape (until you can become a magical beast with a language later on).
I think there's an exception made for turning into a Parrot, but that's it.
At least one of the descriptions for Parrot describes it as not being able to speak as its natural language is a Squawking :)
Not usually, but if your DM rules otherwise I do not see a huge problem. Spell casters turning into speaking animals is not too terribly farfetched and quite common in literature.
The DM can always overrule the books, they probably shouldn't, but they can. (unless the game is PFS)
The issue with casting in beast shape isn't just the verbal or somatic components, but material components. When you polymorph (like wild shape or beast shape) all of your equipment morphs into you new body, including you spell component pouch. Generally speaking, players don't need to keep track of individual components, but they still need to have access to them. A pinch of bear dung doesn't usually seem like an important thing, unil you don't have any.
To be able to cast any spell while polymorphed, you would need eschew materials or natural spell. Depending on your form, you may need silent spell or still spell as well.
He could wear a collar of animal speech and probably accomplish his goal.
Hi character who cast this spell was not a Druid but normal Mage
I realize that. The reason I mentioned the druid's wild shape in my first paragraph is that there's no reason to assume a wizard would function differently in beast shape than a druid would in wild shape (since wild shape is based on the beast shape spells).
Since the same rules would apply, the same limitations would, too. And since a Druid needs feats to be able to cast spells or speak while in an animal form, so would a wizard. Of course, a wizard wouldn't qualify for the feats, so they would be out of luck unless selecting a form with a language.
Just think our DM has not read the rules properly, I have now read the rules about polymorph spells.
Dont see how a collar of animal speech will let a mage who has turned themselves into a creature will let said mage cast spells.
It allows animals to talk. If you wear it and turn into an animal I see no reason why you could not also talk. Additionally it's a continuous effect, so even if it melds with your form it should still function. That at least solves the verbal component though not the somatic one.
At least that's how I interpret it.