I think I've posted all my conlang grammars such that I more or less know how they work. (Laulai was on the edge and needed work to finish it.) Now I have to work out the grammar of the Underspeech. I'm starting from a few words and grammatical constructions like the plural -v combined with changes in the stem. Below, I have tried to reuse parts of the other IE languages I sketched recently. Any advice will be helpful.
The Underspeech is the largest minority language spoken in the seamy underside of Laulai holds. Laulai slang is greatly influenced by it. Natively, the Underspeech is called Myëřëliw "mountain speech". The Underspeech community, called the Zhüüą, believe they originated from the Holy Mountain. (<ü> is [y]. For historical reasons, it's a rule of thumb that initial voiced consonants are pronounced without voicing.)
Many lower class Laulai abductees are absorbed by the Zhüüą because the community is actively evangelistic. Their language is important because it contributes a great extent to the language that will later become Proto-Galactic: viewtopic.php?p=105159#p105159 After the revolution finally overthrew the ancien regime, Underspeech ended up with a higher social status for some time even though it wasn't traditionally revolutionary per se. But since the number of speakers is relatively small, it was eventually absorbed into Laulai like Norman into English.
Each Zhüüą neighborhood is led by a council of "lords". Each lord is called rääh, like in raja. <ä> is [ɛ]. The plural is rääřuv. (Plurals are irregular.) The rääřuv are closer to church elders than lords with real authority. In practice, the council is like a Homeowner's Association. Most people can't afford to tick them off if you live in their neighborhood.
The Laulai demeaningly call members of the Zhüüą böy, which means "child" in Underspeech. The correct Underspeech plurals are böyriv or böy leq "child gang", but Laulai doesn't have a straightforward plural. The Laulai think the lower classes use the plural -s, so they might say böys. This is a coincidence unrelated to any modern earth influence. Despite how it's written, it's pronounced [pœ̀ys]. The <y> is literally the IPA /y/. It may either be regarded as a slur or a testament to Laulai stupidity, being incorrect in any language.
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Religion
The Zhüüą are monotheistic. They worship a god called Zëvnau, where <ë> is [ə]. In the tentative romanization scheme, Zëvnau is pronounced [sə̀vˈnau]. (Note: This religion should not be similar to Semitic religions.) The religion is technically illegal in the holds, but slave religions are not challenged in practice. (Only Pythagoreanism is legal for people, but slaves are not legal persons.) The Zhüüą were brought to space as builders centuries ago and have since then established themselves as the social glue of the underclasses. Even in Laulai, the word for space hold comes from the Underspeech: zevdrǫ.
In mythology, vaguely like in the Silmarillion, Zëvnau sang the world into existence. One of his epithets is Ooną "the Singer". Other epithets include Büünih and Nëbëzhaw. Vocative is uu and comes before the proper noun.
The Zhüüą are skeptical about Zëvnau intervening in the world. After all, they were abducted by "aliens" and now live as slaves in suboptimal conditions. What they have more faith in is that there is uul "beauty" and ëmwuun "harmony" in the world despite everything else. Worship consists in giving gratitude for these elements.
Everyone has the free will to increase beauty and harmony in the world. Art is considered to be an act of worship as long as it's not too subversive (such as a toilet presented as a work of art). However, incorporating ugly truths into a beautiful whole is one of the greatest possible acts of worship. The Zhüüą may be gangsters when they can get away with it, but they aspire to be Bohemian artists in their private lives.
There are several mythological characters. Wine is sometimes represented as a mischievous child with dripping red feet.
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Phonology notes
At this point, Underspeech is an IE language. I'm thinking of the Roma. Perhaps with a vibe like Romanian, Albanian or something vaguely Slavic, with Indic-like grammar. (What if Romani grammar had resembled modern Indic?) I'm considering whether to make the language tonal (really tonal, not marginally like Laulai). In some cases, the syllable-final consonant might indicate tone. (Don't know enough linguistics to pull this off believably.)
Since this is a low speech, maybe I should take zompist's advice and not worry too much about whether I "like" how it sounds. If a lot of words sound like slurs, I'm happy.
I'm thinking that after the Zhüüą were abducted from a medieval IE speech community, the original language died out on earth. Perhaps they were brought over in such large numbers, they didn't have enough people to continue on the surface.
This is my chance to try a bigger vowel inventory than I'm used to. I'm thinking: i, y <ü, y>, u, e, ø, ə <ë>, o, ɛ <ä>, ɔ <å>, a. Plus, there are long, nasal, diphthongs, etc. This is also my chance to represent nasals with the ogonek.
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Vocabulary that has entered Laulai slang:
aiř "iron, hull, ship"
maiq "wage, pay, dough"
vii "guard"
dau "guard" (literally, tree)
greeh "grab, buy, snatch, steal"
bey "fly"
glyääh "rumor, news"
myääh "mountain, upper class neighborhood"
uun ääh "dream water", a drug
maiq leq "laborer gang"
glyääh pim "social circle, information source, informer" (gossip route)
naum ëvöy "foul air of the lower blocks, not literally smoke" (smoke wind)
gräävą "thief, customer, monkey" (grabber)
beą "hotshot pilot, originally non-military but speakers don't care anymore" (flyer)
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Nouns, articles, adjectives
Indefinite nouns are followed by the article öyn [œyn] "one" (like in Bengali, except Bengali [æk] comes first). <ö> is the diphthong [œ]. There is no definite article (like in Bengali).
Like Bengali, numbers have classifiers. (TBD)
Laulai has 10 genders. Underspeech has 0 (like in Bengali).
By default (TBD), the morphology is mostly analytic. Normally nouns use postpositions, but there are two cases, objective and locative. (Additionally, Bengali has the genitive. In the Underspeech, the locative is used for a genitive construction as shown in the "case example" below.)
"Mountain" is myääh.
The objective case is myääřë-ną.
The locative case is myääřë-vę.
(Inflection is irregular, unlike in Bengali.)
Other cases use postpositions (like in Hindi):
eh (ablative)
bii (instrumental, perlative)
ään (adessive)
prai (comitative)
maizh (intrative)
zvii (similative)
Like in Bengali, the objective case is not used if the object is obvious, especially in conversation.
Case example:
Aizhu-vę ääřǫ nyi ya.
At me, silver is not.
"I'm broke (dude)!"
Notes: The first person proposition is in the locative case, being used in a genitive construction. ääřǫ "silver" is related to Argentum and refers to money generally. ya is the copula.
Adjectives come before the noun and are not inflected. The religion teaches that Zëvnau sings an uul oon "beautiful song".
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Verbs, example sentences
Verbs have tenses. (TBD)
"Behold!" is Aiw!
Present tense:
Maiq leq zhel myääřë-vę vi.
"The laborer gang is sleeping in the upper class neighborhood."
Past tense:
Gräävą öyn miny maidu-ną graq!
"A thief snatched my money!"
Future tense:
Tau naivë-vę ai zheem!
"You will go to heaven!" (threat)
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A relative clause opens with i before the noun.
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Some words come from Laulai:
mis "lord" is mih (Laulai lords only)
sen-mis "child lord" is sęmih
serk "true ratio" is serq
ksost "monster" is kësoq
The military organization Mneka is Mëneka
sorm "the reach of understanding" is soom
fot "slave" is foq
Any Laulai word can be used as is. Entire Laulai phrases, sentences and paragraphs can be used as is. This only sounds weird if you don't have an accent or you don't sprinkle in at least a few Underspeech words, expressions and mannerisms here and there. Try inserting schwas in consonant clusters or dropping a consonant and lengthening preceding vowel (like in Bengali). Your performance will sound more convincing if you drop the Laulai arithmological suffixes once in a while. It will get weird again if you robotically never use them at all.
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Underspeech has no dedicated conjunctions. Some postpositions like the comitative can be used instead. You can also put words and phrases next to each other (like in Bengali, though Bengali has conjunctions and they are very much in use). The listener will infer and/or/but/... from context. You can use Laulai conjunctions if you're ok with people seeing you as a tryhard. If conjunctions are that important and postpositions are inappropriate for whatever reason, it might be better to speak that sentence in Laulai.