Southeast Asia is not one market and not one register. A reply that feels warm in casual Bahasa can feel rude in Japanese keigo, and a Thai reply missing its krap/kha particle reads as abrupt no matter how accurate the content.
Politeness is structural, not decorative
In Japanese, keigo isn't an optional flourish — sonkeigo, kenjougo, and teineigo change the verb forms themselves. In Thai, the krap/kha ending signals respect on nearly every sentence. An agent that ignores these doesn't sound efficient; it sounds wrong.
People forgive a machine for being a machine. They don't forgive it for being impolite in their own language.
Code-switching is the default, not the exception
Real customers mix languages in a single message — Indo-English, Singlish, Taglish. An agent fine-tuned only on formal monolingual text falls apart here. It needs to read and respond in the same blend the customer used.
Tune per use case
The right register for a collections reminder isn't the right register for a flash-sale upsell. Localization that lasts is configured per flow — formality, warmth, and slang dialed in for the moment, not set once globally.