His purse is empty already; all’s golden words are spent.

It would be amazing if we had a limited amount of words we could use in a day.
I think I might like to live in such a world. People might be more careful about what they said. They might be more judicious in reporting their news. There would likely be many late night conversations, using up the unspent words of the day. I imagine it might be a quieter world. Especially in the morning, which would suit me very well.

You will do’t, sir, really.

Who is he talking to? If it’s Osric, it seems a little forward. I’m assuming they haven’t met and Horatio’s status may be elevated by being friends with the Prince but he’s not a prince and probably not a lord, either.
But would he call Hamlet sir?
He mostly calls him “my lord.”
I’m very confused about what, exactly, Horatio is saying here and to whom.

Ist not possible to understand in another tongue?

Tongue is a funny word for language and it tends to travel across languages, too. Language and tongue, are in fact, the same words in some languages.
But here – I think Horatio isn’t using the word tongue as language – he’s using it more literally. Because Hamlet and Osric are both speaking English, however arch and verified – but it may SOUND like another language. And I suspect that Horatio is attempting a bit of double meaning with tongue in that capacity.
I don’t think Horatio’s particularly funny, though, or all that quick with words. He’s a better listener than talker.
It is also odd that he pipes up to speak in just this moment.
Has Osric turned to him to get a translation?

No, my good lord.

Horatio does not know Osric. He did not seem to know Rosencrantz or Guildenstern. He seems to have some acquaintance with the watchmen – who are perhaps his fellow countrymen, if their names are anything to go by. Who does Horatio know and who doesn’t he? He mostly doesn’t know people – which is convenient for introducing the audience to them as well.

Who comes here?

And so Horatio echoes the sense of the beginning of the play. “Who’s there?” is not so far from who comes here. It’s a subtle bookend, really. Perhaps, like the opening scene, it heightens the tension before a dramatic event.
Barnardo and Francisco become Horatio.
What’s funny is – after the sentinel’s “Who’s there?” – eventually we get to the ghost.
Immediately following “Who comes here?” – we get Osric. We get comic relief.

It must be shortly known to him from England What is the issue of the business there.

I can’t tell if Horatio speaks in a stilted manner on purpose or if I’m reading more stilted-ness in his language because the first Horatio I worked with had a bit of brain damage and had to do a little extra work to sound like an authentic person. I thought maybe I was projecting that stiltedness from that first performer but this line is stilted.

It actually has the flavor of a non-native English speaker – which is, of course, a theory I’ve floated before. Horatio doesn’t have a Scandinavian name, he doesn’t know the customs of Denmark and often has to ask about obvious things. The fact that he rarely has a line that isn’t a follow up of the previous line or a simple question also suggests someone communicating in a language that is not his first.

Certainly, when I learned Italian, some of the first successful conversations I had featured lots of things that allowed the other person to keep talking and thereby took the burden of language off of me.

This slightly more complex thought may be revealing more of Horatio’s growing skills in English/Danish.

Why, what a king is this!

This is a very odd moment for Horatio to exclaim like this. He’s not really directly responding to what Hamlet just said; Hamlet was just talking about Rosencrantz and Guildenstern and only obliquely referred to Claudius, if at all, as one of the mighty opposites. (Maybe.)
So…this exclamation from a man who mostly just nods along and supports Hamlet – is very out of character and out of sync with the conversation.
Some have theorized that maybe Horatio means Hamlet but Hamlet is not King. He’s a Prince. And if it were about Hamlet, wouldn’t it be “What a King you’d be!”?
I could buy it as an exclamation of praise – the way a friend might call me a queen when I do something with authority.

So Rosencrantz and Guildenstern go to’t.

So do we all, eventually. Though hopefully not to an execution the way they are.
I have always been spooked by execution. I used to have nightmares as a teen in which either one or the other of my parents had been condemned to execution for reasons that were not clear. The state, the authorities, the government seemed more powerful than any other means of death I could imagine. More intractable. More – immovable. My protests more desperate – a hope for justice still bumping around in the dark like a moth.
Rosencrantz and Guildenstern don’t endear themselves to many in this play – but the notion of anyone getting executed freaks me out a bit.

Maybe they escaped?

Maybe they were killed by sea pirates instead?

How was this seal’d?

This question suggests an unusual amount of knowledge of royal messengering. Unless, somehow, it was common knowledge that a seal on an envelope sealed its authenticity. I mean, how many people actually received royal communiques? How many people had even seen a royal seal? But, Horatio is friends with a prince and even when Hamlet’s not there, he hangs around with royals so I guess he’s got a lot of insider knowledge of how this stuff works.
But also I wonder if he hasn’t secretly plotted such a thing and this question speaks to an obstacle he encountered, so he’s thought it through. Maybe.