This feature is not on a current W3C standards track, but it is supported on the Firefox OS platform. Although implementations may change in the future and it is not supported widely across browsers, it is suitable for use in code dedicated to Firefox OS apps.
readyState property returns either
complete — depending on the current state of the L10n context.
var readyState = navigator.mozL10n.readyState;
console.log('Localization is ' + navigator.mozL10n.readyState);
Not part of any specification.