My supervisor invite me to spend the Chirismas eve. But I do not like to go. How to write the email to refuse his invitation politely? Thanks.
This is only my guess, but I'd want to learn to write these polite replies, too.

Dear Mr. ***!

Thank you very much for your invitation to spend the Christmas eve with you, I was very pleased to recieve it. Unfortunately, I have already promised to my friend [family, colleague, spouse etc] to attend his place on Christmas day, so I will not be able to accept your invitation. Please accept my apologies.

Merry Christmas to you and your family and happy New year!
Sincerely yours,

Is it ok?
Send the message that reads

I need to spend that night with my mother or father. She or he isn't
in good shape.

A small lie sometimes works.
Students: We have free audio pronunciation exercises.
Pieter, your version was great! Really!Emotion: smile
your letter is very courteous........unfortunately you don"t need to apologize with them...........b ut tell hem the truth.
You may also state ' I am honoured by your invitiation, I am afraid that I wont be able to attend'

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actually it is not the right answer.Emotion: yawnEmotion: embarrassed