-Translator devices are used by everybody, because the communication organs and systems are too different to speak a common language. Which also means that an output part is unnecessary, just a smaller device being attached close to an ear.
-Serkanians look closer to the ancestral creature I once drew up. Horizontally oriented, arms and legs looking more similar to each other, the tail with a specific curling direction and padded underside, the head more elongate, considering it's the old head with three limb segments fused to it and shallow eye sockets with the eyeballs being mostly external, both for greater mobility to make up for the fat, stiff neck and to interfere less with the teeth, muscles and support structures of the skull. The antennae are purely for communication and tactile sensing, no metaphysical weirdness here. Clothing was adapted to the new posture.
-Idraths have a shorter torso and larger postabdomen, giving them better stability and allowing for quick turns. Other notable changes are flanges on the abdominal segments and above the jaw joints to protect underlying structures and the chin spikes being in line with the upper jaw's extensions. Also, the thoracal plating got reworked with the arms attaching to the chest plates and the joints hopefully make more sense now, as well as being more mobile.
In this depiction, they are small devices glued close to one's ear. A microphone receives sounds and if the AI recognizes the sounds as speech in any of its recorded languages, it will give out a translation with some delay. In the actual story, where a common language is spoken by most, the devices consist of two parts, with the aforementioned input part, but also an output part, which is a louder speaker usually strapped to a limb. There, the translators only do one language at a time, which has to be decided in its settings beforehand (if the language is unknown, it can be set to analysis mode, where the AI identifies the language spoken).