Deprecated: This feature is no longer recommended. Though some browsers might still support it, it may have already been removed from the relevant web standards, may be in the process of being dropped, or may only be kept for compatibility purposes. Avoid using it, and update existing code if possible; see the compatibility table at the bottom of this page to guide your decision. Be aware that this feature may cease to work at any time.
Non-standard: This feature is non-standard and is not on a standards track. Do not use it on production sites facing the Web: it will not work for every user. There may also be large incompatibilities between implementations and the behavior may change in the future.
The locale read-only property of the CompositionEvent interface returns the locale of current input method (for example, the keyboard layout locale if the composition is associated with IME).
Warning: Even for browsers supporting it, don't trust the value contained in this property. Even if technically it is accessible, the way to set it up when creating a CompositionEvent is not guaranteed to be coherent.