英语翻译当你收到这束花的时候,很高兴地告诉你,有一个人想约你看电影,时间是今天晚上.如果你今天晚上没有约会的话,他很希望

Your translation is basically alright.However,It needs a bit of fine-tuning.
When you receive this bouquet of flower,I am glad to tell you that someone would like to go see a movie with you tonight.If you are not busy tonight,he hopes that you can go.
"this flower" refers to a single stem of flower unless you have indicated before it is a bouquet and use "this" here to refer to those flowers.Alternatively,simply use "when you receive these flowers".
There is no need to use future tense for "I will be glad".If you want to be more polite,use "I would be glad".
Want sb to do sth is more a demand than an invitation.Use "would like to go" or "would like to invite you to go".
Go see a movie/ go do something.There is no need to say go to see.
"he hopes that you can go" instead of come.The invitation is from a third person or presented as so.If the subject of this sentence is I,you can say "I hope that you can come."
I also provide an alternative for your reference:
I am pleased to tell you that as you receive this bouquet,someone would like to invite you to a movie this evening.If you are available,he looks forward to seeing you then.