もしあればレモンを入れて欲しいって英語でなんて言うの？

Could I please have some lemon with my tea? Standard request, if it is obvious that the place has the goods then it is a simple question. You can change lemon to milk/sugar etc. By any chance, I don't suppose you have any lemon do you? Very polite! On a place such as a plane where sometimes they will not have it and even if they do but won't give it to you. This is the best way to get what you want. Is it possible to have a little lemon/milk with my water/tea/coffee? Polite. You may ask your server this and 9 times out of 10 they will be able to meet your request.

When you go to a restaurant it is important that you are very specific so that you can get exactly what you want. *Can I have some hot water with a slice of lemon please.- This mean that the slice of lemon will be in the cup with the hot when it comes. *Can I have some hot water with a slice of lemon on the side please.- This mean that you would like the hot water and the lemon must not be in the hot water but in a side plate then you will put it yourself.

A 'squeeze of lemon' - Unfortunately there are a few crude connotations with this phrase and it may be best to avoid it. For example, it may mean when a man squeezes a woman's bottom; or when a someone urinates in the morning! However, you can safely say: "Could I have a lemon slice with that please?"

If you want to have some lemon in your hot water then you could ask 'can you put some lemon in it, if you have any?' or 'do you have any lemon i can add to it?' a polite way of asking is 'is it possible to have some lemon in it please?'

"Do you have any lemon for the water?" This asks if they have any lemon and if they do could you please have some in your water. "Can I lease have lemon in my water?" This asks them to please give you some lemon in your water.

a squeeze of lemon - this means just one or two squeezes, so a little bit of lemon in it May I have (something), please? - this is a polite way to format your question or request

When I order this drink I usually just say 'hot water with lemon please' and that should be enough, however if the waiter doesn't understand, you can be more specific "can you add a slice of lemon to my hot water".