There are two types of Japanese phonetic characters, and Japanese keyboards have Katakana mode and Hiragana mode for them in addition to alphanumeric mode. Also, there is another type of keyboard modes, SBCS mode and DBCS mode. Since there are many keyboard modes, the current mode should be displayed so that the user can keep track of which mode they are in.
The WC_DBE_KBDSTAT control is needed for users to avoid confusion. Once you supply this control to a standard window, the system will automatically update the contents of the control according to the current shift status of the input queue belonging to the window. [The shift status specific to DBCS countries is maintained for each application input queue. The alphanumeric shift status such as caps lock is maintained for the whole system. ] Therefore you do not need update the control.