With its regular grammar, unambiguous pronunciation and spelling, and defined vocabulary, it is trivial to translate into Standard. In fact, thanks to the universal translation available throughout the Mess, outsiders rarely even notice that someone is speaking or writing in Upstandard rather than Standard. Translation in the other direction can be quite a bit harder, since it strips away as much ambiguity and idiom as possible.
Upstandard arose as a few Upwarpians became dissatisfied with Standard's eccentricities, and overwhelmed with the continual deluge of newly coined jargon and slang, and loan-words from outside languages.
Its grammar and vocabulary is defined by the [Up/Department of Linguistic Standards]?, a body which reviews new concepts and coinages in other languages throughout the Mess and approves them (or suitable alternatives) for use in Upstandard.
Feel free to play with this one, or correct it. I don't know, for example, if it is or should be official within the Warp, or simply a project of some local enthusiasts. Theme Functions?
It's along the same lines as [Lojban], and to a lesser extent [E-Prime], not to mention [Latin] as a universal language among learned Europeans throughout the centuries. I'm not going to define its grammar myself, 'cause I can't be bothered. ;)
The Department of Linguistic Standards is inspired by the [Académie française] and the [Office québecois de la langue française].
I once ran across an older English translation of a racy story from another language and was amused when it switched - in mid-sentence - to Latin for what was apparently the naughty part. I wanted very badly to steal that idea too, but I can't figure out how. Maybe the Vickies have their own 'high tongue'?