Would the best way to translate "You are at war" be "Vos es in bellum"?

Many thanks in advance.

Hi there!

By "you are at war" do you mean singular or plural?

Not 100 %, but:
singular/2 >>tu es = you are
plural/ 2 >> vos estis = you (you+he+they, etc)
in / at something >> in + abl
bellum word in ablativus>> bello (I don't have the correct character on my keyboard, but that o letter has a - mark on its top (cuz it's a long letter).

if singular it should be:

Tu es in bello.

If you mean plural:

Vos estis in bello.

The verb bellare means 'to wage war,' so 'you are waging war' / 'you are at war' would be:

(tu) bellas = singular
(vos) bellatis = plural

You don't need the tu / vos (the ending on the verb includes the 'you' already), but you can include them for emphasis.

Thank you, gentlemen.

I was looking for the singular "you". I'm making an inscription on something, and this will do nicely.

Simply "bellas" would be appropriate. You could add "Tu" before it to make it more formal, but because it is already in the second person, the "you" is implied. adding "tu" would not be redundant so much as giving it emphasis.
Also, adding the long dash over the "o" to denote ablative is used as a guide for people learning Latin because it is pronounced differently (long), but it is not generally written that way on inscriptions and formal writing.
Also, Latin is a nice language in that word order is not critical to grammar. However, proper etiquette is to place the verb at the end, so if you want to go with the larger phrase the most appropriate way to write it would be (Tu) in bello es.
I just completed my Latin Minor at my university, so while I am not an absolute expert, this information is also still fresh on my mind.
Good luck,
Quinn

Yeah, I learnt latin in secondary school, and 4 years have passed since I opened the grammar book :D Seems I already forgot how to spell things in that.

I'd translate it in the passive tense, particularly if you mean it as a threat, the way I think you do.

"You are being made war upon" = "BELLARIS" (1st conjugation, 2nd person singular, present, passive)

This way, you get the bonus meaning of: "If you can read this, then I'm going to kill you."

That's a good call on passive voice. I know it sounds a little awkward in the translation, but passive voice in Latin is not "weak language" as it is often considered in English.

Lewis and Short says that bellor is a deponent verb, meaning that in this case the active and passive voices would mean the same thing.

For the non-Latinists reading this, that means that bellas and bellaris are two ways of writing the same thing. Both communicate the idea of waging war (actively).

I mostly do Greek (Latin was 25 years ago), but isn't it elegant Latin style as well to minimize the word count?

I don't know what would be more appropriate for medieval Latin - L&S says that the deponent form is rare, but that's referring to classical Latin.

Of course - if we're talking about a medieval sword, odds are good that the craftsman didn't know that bellaris is deponent. He could probably invent a passive without anyone upsetting anyone.