Braces are usually fitted on the front surface of the teeth and are visible when you smile, but they do not change your speech. This is because sounds are formed by the tongue touching the inner side of the teeth, the palate and the lips. If no appliances are placed on these surfaces, your speech is not expected to be affected.
There are also lingual braces, which are bonded to the inner side of the teeth for better aesthetics. These can affect speech, but the tongue adapts quickly and patients get used to them within a few days.
Aligners are thin, rigid, clear trays that cover the teeth both on the outside (the lip side) and on the inside (the tongue side). They can also change your speech slightly for the first few days after you start wearing them, but you adapt fairly quickly. To get used to them more easily, it helps to read aloud regularly and talk as much as you can.
This answer is for general information. Your own case needs an examination by an orthodontist.