The Bluetooth word mark is a trademark, and as such its spelling
cannot be changed. It is always to be used in either English, its
Traditional Chinese translation “藍牙”, its Simplified Chinese
translation “蓝牙”, its Japanese translation “ブルートゥース”, or its
Korean translation “블루투스”; it must not be translated into other
languages.
Ref:
Wikipedia
Brand Guide for Bluetooth Trademark