As short examination of the Gothic language

While the Imperium has almost as many languages as it has worlds, most citizens are reasonably able to converse in some variety of Gothic; indeed, many of the tongues spoken on a given planet will be nothing but heavily isolated and bastardised versions of this language.

The Gothic tongue was developed in the period of humanity’s expansion across the galaxy and is named after the Gothic sector, closer to the galactic core and an ancient and important hub sector in Segmentum Obscurus. The language was originally a creole composed of various languages from Holy Terra (including such long forgotten, archaic tribal tongues as Hindo-Yuropian, Chino-Dhibetan, Chipanic, Yndonesic, amongst many others), but it is far removed from those roots and would be next to unrecognisable to speakers of those archaic tongues.

High Gothic is the variety of the language used by academics, nobles, administrators and the priesthood. It features in most scholarly works and has a standardised spelling. The uniformity of High Gothic is ruthlessly maintained through the schooling of its users, and thus two speakers of High Gothic from different parts of the galaxy can communicate without any hindrance.

Low Gothic refers to any local and/or colloquial variety of Gothic, and is thus actually a group comprising many different dialects and what one could even consider separate languages (although many are usually understandable among interstellar travellers, if with some difficulty). The most common variety in the Calixis sector and the Koronus Expanse is Calixan Gothic, which is largely similar to the Gothic spoken along the warp lanes across Segmentum Obscurus. Most variants of Low Gothic incorporate a great many Techna-Lingua loan words (much to the chagrin of the techpriests of Mars). Many are also peppered with slang terms and expressions loaned from local languages or simply unique to their own cultural context.

Some other commonly heard varieties of Gothic:
Trader’s cant: An extremely stripped down pidgin Gothic used when haggling across the linguistic barriers of the larger ‘Gothics’. Includes a wide variety of nuanced ways of discussing wares and prices, but is understandably short on terms for emotions; however, it has several very creative ways of insulting the commercial practices of one’s conversational partner.
Soldier’s cant: Shortened forms most often used for battlefield communication. Include plenty of colourful terms for death.
Void cant: The language of voidsmen. Contains many expressions peculiar to this group, many of them pertaining to the nature of a ship’s environs, the activities of the crew and the void itself.
Ship dialects: Dialects confined to specific vessels or smaller fleets.

Some Gothic idioms and terms from various sources:

Calixan Gothic
“to have a day on Klybo” = to have a hard time (also, “it went like Klybo”, as in “to have a complete disaster”, as in the famously disastrous colonising attempts on the planet Klybo)

Military terms
“the Emperor’s Benediction” = euphemism for mercy killing in the Imperial armed forces
“brain”, “freak”, “bolt magnet” = enlisted man’s term for psyker (psykers instead sometimes refer to normal humans as “blunts”)
“to be found wanting” = field execution of a guard soldier or navy voidsman by a military commissar (as in “He was found wanting at the front line.”)

Common Low Gothic Expressions
“plank” = idiot (originally specifically an ogryn, i.e. a near-human from a heavy gravity world)
“twist” = derogative for mutant
“Catachan kiss” = a headbutt (so named for the typical unsophisticated behaviour of people from the death world Catacha)
“grox dung” = something bad; from the grox, a species of tough saurian cattle husbanded mainly for their meat (similar in function to Terran cows and oxes); also used to indicated stupidity or physical prowess, as in “dumb as a grox” or “strong as a grox”

Void cant expressions
“to be born out airlock” = to be an idiot (“Where you born out of airlock, or did you do something in particular to become this moronic?”)
“system pirates” = same thing as “second rate”; (in)system pirates are inferior to interstellar pirates that travel the stars (cf. the ancient Terran expression “freshwater pirate”)
“asteroid humper” = derogative for asteroid miner
“hullgeist” = a stowaway on a ship, living in the spaces between hull compartments. Often mutants and the like.
“void, the” = space, vacuum. Also about space suits and similar items: Voidsuits, voidsteel, voidcraft.
“augur ghost” = inexplicable returns on a augury reading (‘augurs’ refer to ship sensors). Often considered a bad omen.
“a one day leave” = dying from starvation, especially aboard a crippled ship; from the fact that standard imperial emergency ration packs aboard void vessels only last one day, since if help has not arrived by then it is unlikely to arrive at all. Contrasts with ‘24 hour leave’ or ‘standard leave’ which both describe a one day period of leave, without implying death by starvation. Usage: “Poor Clavius took a one day leave, so we’re a hand short.”
“to the cherubs” = something that has gone bad or broken; from the cherubim servitors that maintain many of the ships systems and the way they typically flock to any problem. The cherubs themselves are thought of by many voidsmen as ill-omened and the eyrie-alcoves where they rest are avoided by all but the techpriests who tend to them.

As short examination of the Gothic language

Opus Imperatoris, Homines Voluntas gatusamurajen gatusamurajen