01
The service is too slow.
服务太慢了。
A: Can you tell me what's wrong, sir?
能和我说说有什么不妥吗，先生？
B: The service is too slow and the dishes are served cold.
服务太慢了，菜都凉了。
A: I see. I'll report it to the manager.
我知道了，我会把这事告诉经理的。

02
There is too much salt in the soup.
汤太咸了。
A: Is everything to your satisfaction?
您对饭菜满意吗？
B: Yes, all the food was delicious except that there is too much salt in the soup.
是的，除了汤太咸之外，所有事物都不错。
A: I'm so sorry for that. I'll take it to the kitchen and get you another one if you like.
真对不起，如果您愿意，我拿到厨房再给您换一下。

若饭菜质量有问题可向服务员提出意见。还可以用“There's something wrong with...” 表示“某事或某人有点儿不对头”
The meat is underdone.
是说肉没熟。而overdone则是“过头了”
I'm afraid this is too salty/sweet for me.
我觉得菜太咸/甜了。
That's not what I ordered.
那不是我点的。

要提意见应该说：
I want to make a complaint.