R@re! wrote: Mir ist kalt.
The subject isn't in nominative and the verb is conjugated in third person singular. My question is, if I want to change the pronoun does it mean I would have to conjugate the verb as well? Do you know any other such expressions in german?
There is no subject in this sentence. You can add a dummy "es" subject if you want (this is the more natural version in my dialect), which would it make look more like a regular sentence: "Mir ist es kalt". Accordingly, it's always "ist".
This construction is only used in a few cases. Apart from temperature ("mir ist kalt/warm/heiß"), I can only think of "mir ist schlecht" at the moment. There are probably some more, but not many.
Es ist nächsten Winter.
The adjective is in acusative here. Why?
It's just how time specifications work when there is no preposition.
Das Fest war letzten Monat.Diesen Sommer fahren wir ans Meer.Er kann jeden Augenblick kommen.Accusative is also what you use for the date in a letterhead, e.g. "Stuttgart, den 4. April 2020".
Euer ernst?
Can I use other pronoun instead of "euer"? I think this would translate as "You serious?"
This is a colloquially shortened form of "Ist das euer Ernst?" (Capital "E", it's the noun "Ernst", not the adjective "ernst") The same shortening works well for "Dein Ernst?" and I don't think there is anything that would make it impossible for other pronouns either.
Stop it you donkey!
Can I translate it word for word?
I think I would understand the English as meaning the same as "Hör auf, du Esel!", but I'm not sure about the exact meaning or connotation of calling someone a donkey in English.