There is currently no querying of the X Window manager to see whether
dynamic layout is supported or not. The current code looks like this.

/*
 * Class: sun_awt_motif_MToolkit
 * Method: isDynamicLayoutSupportedNative
 * Signature: ()Z
 */
JNIEXPORT jboolean JNICALL
Java_sun_awt_motif_MToolkit_isDynamicLayoutSupportedNative(JNIEnv *env, jobject
 this)
{
    switch (awt_wm_getRunningWM()) {
      case KDE2_WM:
      case SAWFISH_WM:
        return JNI_TRUE;
      case CDE_WM:
      case ENLIGHTEN_WM:
        return JNI_FALSE;
      default:
        return JNI_FALSE;
    }
}

Since dynamic layout is often a user setting, we need to query the WM
to see what the setting is.