Right. PIE is a conlang that is a "semi-mythical recreation" of the Ur language that linguists imagine that all European and Indus languages must have evolved from. It's mostly guesswork but provides a sort of framework. That article wasn't the best example or treatise on the topic, by any means, but more of an introduction so you could all know what I was talking about.
The base of it is: it has all tenses, cases, and declensions that exist in every Indo-European language. All pronunciations (which really wouldn't be used here very heavily) are amalgamations of the best-guess of the word's true etymology.
Really it just gives an idea of what a language must contain to be considered as complete as possible, and to evolve into many multiple languages.
Honestly, I'd be happy if the languages just seemed related to each other
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You "could" get rid of the 2nd person plural, but that forces the language into agreement with Modern British English in a rather arbitrary way. Even we Americans have found multiple ways to add that back in ("Y'all", "You'ns", "You's", "You's guys", etc) since it often comes up that one must talk to a group of others that is physically present, and make it clear that you, the speaker, mean ALL of the assembled group instead of a specific person.
Besides, in actual speach, "-te" (pron: Tay, rhymes with "they") and "-ti" (pron: Tee, rhymes with "He") don't sound very similar at all. It would make more sense if the conjugations were more regular tho:
1s: -mi 1p: -mos
2s: -si 2p: -sos
3s: -ti 3p: -tos
ORMOS! <-- Theoretical Dwarven equivallent to "Cheers" or "Na zdrovyeh" (lit. "We Drink!")
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The conjugations would be something that could probably best be defined per-entity. That would allow maximum versatility, and let each language sound more unique. Plus, it would allow, say, the human entity to drop certain types of conjugation for, say, nouns or verbs individually, allowing for a "dropped second person plural" if the creator of that language so wished.