Ok but i figured it out though:
In 1.10 the last parameter in addInformation was a boolean value,
Now it's a class called ITooltipFlag
@Override
public void addInformation(ItemStack stack, World playerIn, List<String> tooltip, ITooltipFlag flagIn) {
super.addInformation(stack, playerIn, tooltip, flagIn);
tooltip.add(TextFormatting.GRAY + "" + TextFormatting.ITALIC + Util.getLang().localize(getUnlocalizedName() + ".tooltip"));
}