Help Please

[Peter Harvey]

If anyone can help me out with this card it would be appreciated:

Country of origin?
What does the cachet say?
Any idea of the message details?
Addressed to and from?

In other words, I don't have a clue?

Thank you

[Sozont Singh]

Peter, hi!
It is one of the Slavic languages (I believe Bulgarian). I will try to roughly translate. The sender is "rotmistr", which can be roughly translated as a captain, his surname and the word is not clear and he is in 5th division. He sends a letter to Sofia, the capital of Bulgaria, on San Stefano street. Now I'll try to parse the main text.

[Sozont Singh]

The card itself says a military postcard. At the bottom, an indication that if any military secret is contained, then it must be destroyed.
Stamp, as far as I can understand, the Bulgarian Danube division.

[Sozont Singh]

On the other side is the following text:
December 20, 1915
Brother Dimo (this is a variant named Dmitry)
Merry Christmas and Happy New Year.
I wish you health and (the word is not clear).
Give my regards and congratulations to (further indicated to whom).
Then he asks for something. At the end, probably, some wishes and a signature. These two sentences are not clear to me at all, unfortunately. I have never read Bulgarian before.
At the university, we studied the old Slavic language, which is the basis for the later Slavic languages, so in general I can understand, but I don't understand here anymore.
I hope I could help at least a little :-)

[Peter Harvey]

Hi Sozont,

First sorry for the delay in reply, I am very busy with some family matters.

Your help was fantastic, thank you, I would not have understood so much without your translation, I thought Bulgarian, but was uncertain and I certainly would not have been able to read the reverse.

I hope you are well.

Peter

[Sozont Singh]

Peter, hi!

I'm glad my little translation helped you!