From RAW
When a creature’s hit points drop below 0, it becomes unconscious. When a creature’s hit points reach a negative total equal to its Constitution score, it dies. -- Core, page 12 under 'Hit points'
'Creature' would imply that the rules effect everyone.
Although there are some exceptions, such as Undead and Constructs
Not at risk of death from massive damage, but is immediately destroyed when reduced to 0 hit points -- Bestiary page 307 and 310 under Constructs and Undead traits
But from a GMing standpoint it won't make much difference to house-rule 'minions die at HP:0', unless your group likes to take prisoners.
Languages don't come from stats, ability scores, or skills. They come from race, and possibly from class or background.
Languages
By virtue of your race, your character can speak, read, and write certain languages. (PHB p.17)
From their first mention languages are set out as a racial benefit. Two exceptions arise--Druidic and Thieves' Cant--as class benefits. Later, we see that knowledge of a language may arise from a background (p.125) or from extensive training (p.187). Which gets us to my interpretation:
Languages are part of your deep background.
Language acquisition as a racial feature arises from assumptions about segregated communities; the DMG (pp.20-21) discusses ways in which one might adjust these assumptions and how that might impact language acquisition. (They give the example of a racially-blind kingdom-dependent language system as an alternative.)
Language acquisition as a class or background feature is more-explicitly based on long times spent in the relevant community/diverse settings/life of study. Note the acolyte and sage gain two languages; guild artisan, hermit, noble, outlander each gain one. Alternately, you can pay to train for 250 days and 250 GP. This also constitutes a large amount of time, effort, and investment on the part of the character.
Thus, changing your ability scores, statistics, or skills have no effect on your languages. Because those changes haven't changed your experience, by which you acquired language. (Admittedly, those changes might impact your ability to hear, speak, read and/or write, however.)
Languages aren't a skill. They aren't tied to an ability modifier and your broficiency bonus in that way because they're binary: you can't (RAW) be more- or less-skilled in a language.
Languages aren't pegged to attributes. But they used to be. Originally PCs were guaranteed two languages: common and alignment. INT>10 made it possible to know more languages. In 1e your intelligence capped the number of languages beyond your base (racial/class) languages that you could know. In 2e your intelligence capped the total number of languages that you could know, all the way down to INT=1 capping you at zero languages: "while unable to speak a language, the character can still communicate by grunts and gestures." (PHB1e p.10, PHB2e p.16)
[ed.: I'm working off of retroclone material for the Original cite: if anyone's got a good cite to edit in I'd appreciate it.]
Is it related to personality? Personality isn't really a defined term in D&D, so this gets sticky, fast. For our intents I think it's easy enough to say "no," but recognize that language and personality formation are interwoven in real life in a way our game just isn't trying to simulate.
Best Answer
They don’t, no. I mean, arguably, they could just have a really short list of options for bonus languages—those lists aren’t printed anywhere for most (any?) monsters, and it could result in not being able to learn new languages even if your Intelligence would otherwise entitle you to some—but really, the answer is just no. They do not follow the same rules, they just know the languages they’re written up with.