function _setCurrentLanguage(newLanguageId) {
        var oldLanguageId = currentLanguageId;
        if (oldLanguageId === newLanguageId) {
            return;
        }
        currentLanguageId = newLanguageId;
        PreferencesImpl.manager.signalContextChanged(_buildContext(currentFilename, oldLanguageId),
                                                     _buildContext(currentFilename, newLanguageId));
    }
@private
This function is used internally to set the current language of the document.
Both at the moment of opening the file and when the language is manually
overriden.

@param {string} newLanguageId The id of the language of the current editor.