Congratulations on your discovery of Rilke and I'm not surprised that you fell in love instantly with his poetry. There may be no writer who did as well to capture in writing the sound of spoken verse as it bypasses the prefrontal cortex and goes straight to the limbic centers of the brain. Goosebumps and a sugar rush at the same time!
This untitled poem first appeared as part of a collection of Rilke's poems titled Advent in 1898, when Rilke was in his early twenties.
Subsequently it was included in a larger collection titled Erste Gedichte which was published in 1913. (Facsimile of the page with the poem in the first edition.)
I am curious, however, why the last line in the translation you link seems slightly out of place to you. The three words
Du gehst mit
at the end have a granite yet intimate quality to them. Unadorned, they call to mind the nudity and vulnerability of a lover drawing close to the beloved. Unrefined, they stand like a boulder blocking one's path.
Just as in German, second person singular is an unusual point of view in English writing. One usually shies away from such a direct approach.
Let us go then, you and I,
When the evening is spread out against the sky
starts T. S. Eliot's The Love Song of J. Alfred Prufrock (1915), and it does not get any more direct as it progresses. Almost instinctively, we (English speakers and German speakers alike) shy away from bluntness and look for circumlocutions instead, but not to the same extent. The difference may not be large, but German does seem to have fewer inhibitions about breaking that taboo.
wondering if the original German is an imperative, or a request, or future tense
An excellent question, hits the nail right on the head.
I would say, Yes to all three of them!
However, it is curious, isn't it, that the last line is not
Du kommst mit.
Robocop, if I may lower the tone for a moment, says
Dead or alive, you're coming with me.
This is actually stronger than a direct order. Robocop does not even contemplate refusal, it is already a foregone conclusion that what he says will happen shortly. "You're going with me" would not carry the same force: "going" implies that the person addressed still has a choice. And with someone as careful to weigh his words as Rilke, this is no accident.
But wait, that's not what the translator chose!
You come too.
It has the same lapidary quality as the German... but something is different now. While
Du gehst mit, in shifting focus to the beloved, vouchsafes volition to her,
You come too keeps focus on the speaker's point of view, and thus sounds rather more peremptory and less dreamlike than Rilke most likely intended.
So I find myself agreeing with you: there is something "off" about the translation's last line. I would rate it as the work of a talented amateur.
Oddly enough, there appears to be no published English translation in book form of the poem, or if there is I haven't found it. However, I came across this translation on the Web by a writer named Hadi Deeb. The difference between the translations is large, not only in style -- one can always argue about artistic choices -- but in quality. This guy knows what he is doing. And of course, he does not flub the last line, either:
That you would dream to go with me.
And yet, and yet... there is something worth preserving about the use of the second person singular present tense (not present continuous) as a request -- in English even more than in German. The amateur's translation, while mixing up "go" and "come", stayed faithful to that. Whereas the pro, as beautifully realized the meter in his translation is, nonetheless gives up on this quality. For an example from an entirely different domain demonstrating how the sudden use of 2nd person singular in this way can shift the tone, watch this Youtube video starting at around 6:05. Feel the tension mount until about a minute later... the use of 2nd person singular for a commandment relieves tension and shifts the tone.