Even Duolingo will tell you that
Greetings and other similar expressions are often shortened versions of longer phrases, where words still retain their forms.
When you see an oblique form (i.e., a declined form) of a phrase, it is an indicator that it is often part of a longer phrase and one in which the declination makes grammatical sense.
So, maybe if I knew the fuller expressions of these Russian phrases, they would make more sense to me. Below you will find what confuses me about these phrases:
This latest exploration into Russian all began when I tried to figure out how to literally translate the phrase:
С днём рождения!
word-for-word/literally. I then wondered why the "c" was even used at all. I then realized I really didn't know for sure what the literal meaning of this phrase was. I then noticed that
Happy Easter! ∼ Счастливой Пасхи!
I got to wondering, If this is a shortening of the longer phrase "I wish you a Happy Easter!"
Я желаю вам счастливой Пасхи!
then shouldn't "happy easter" be in accusative case? And if so, and Пасха is feminine, then why isn't Happy Easter!:
What case is "Счастливой Пасхи!" in? I am assuming both words are in the same case, but if I am mistaken, please let me know that, too.
Furthermore, if a form of the word "счастливый" is used to express "Happy Easter" why isn't it used when wishing one a "Happy Birthday"? Is Easter the only holiday that uses "счастливый" for a greeting such as this?
Happy New Year's appears to mirror the Happy Birthday construct with:
C новым год!
but again, how does this break down literally, and why not use a form of "счастливый" to express it?
Merry Christmas appears to use both forms if Reverso is any indicator
but again I'm not entirely sure about the literal breakdown or use of case.
Are there any other holidays Russians typically front with "Merry" or "Happy"?