Been entertaining myself with that perennial favorite, teaching myself new languages from random documentaries on YouTube. Bunches of episodes of Mystery Diagnosis on this playlist have foreign language subtitles; the Dutch ones are old hat to me now, but the handful at the start are more interesting.

Mind you, I don't have the foggiest clue what language this actually is. For all I know it's Lower Venusian. I'm just doing crypto here.
The subtitles are not an exact transcription/translation. Please do not ask me how I know that when I can't actually read any of it. The triggers for some of these language alerts are unknown even to me. Half the time I'm just reporting when they go off.

Written in the Roman alphabet. Lets out Russian, Ukranian, Bulgarian, and a bunch of other things from Eastern Europe, all of which use the Cyrillic alphabet. Also lets out Farsi, plus Uzbek and some of the other Turkic languages, which use Arabic script. Also not Georgian or other feisty regional languages, which I suspect maintain their own special scripts mostly to spite their various would-be conquerors.

No barred-L. Not Polish.

No dotless i. Not Turkish.

No umlauts. Not German, Hungarian, or any of the Scandinavian languages, including Finnish and Estonian.

No doubled vowels. The position of J indicates that it is a vowel in this language, but the digraph IJ does not seem to exist. Not a dialect of Dutch, Danish, or Flemish.

Extensive use of K. Not a romance language. Spanish, French, Italian, Portuguese, Romanian and others in the family admit to the existence of K, but use it only for loanwords.

C-caron, S-caron and Z-caron all exist. Given some of the medical terms that are obviously loanwords from English or a Romance language, S-caron says "sh", which means an unmarked S probably says "s". (Not always the case -- in some Eastern European languages unmarked S says "sh" and unmarked C says "ch"; the diacritical marks soften them into "s" and "k" ot "ts" respectively.) This suggests a couple of common diacritical transformation patterns, in which C to C-caron either goes from "k"> "ch" or "ts" > "ch". Z to Z-caron may be "ts" > "zh" or "z" > "zh".

There are enough random small words to be prepositions. Many of them are consonants which have been allowed to wander freely about, unsupervised by any of the usual vowels, and are not linked to either the preceding or following words with an apostrophe or dash or any other indication that they are a contraction of something else. Suggests that this is from one of the chronically vowel-poor regions of Eastern Europe.

Some of the other small words may be various cases of pronouns, copulae, or forms of to be/to have/to do, which are almost universally hideously irregular in conjugated languages. Not all languages conjugate verbs for subject, but given how many words I see with an -a, -o or -i ending in roughly the same relative position within sentences, I am guessing this one does. These may be different tenses or moods, or the language may have different classes of verbs that conjugate slightly differently, like the -er, -ar, and -ir verbs of Spanish.

The language is heavily-cased. Proper names pop up with suffixes a lot, which change depending on where in the sentence they occur. At minimum, it has accusative (direct object), dative (indirect object) and genitive (possessive) cases; the existence of the nominative case (no ending/standard dictionary form, subject) is assumed. Nouns also seem to be inflected for number; there's a one and a more-than-one at minimum. There's also an ending that makes nouns into adjectives. Likely there is also at least one that makes adverbs.

I am undecided as to the extent of Latin influence on this language. On the one hand, "ki" and "ko" seem to function as "[that] which/who" and "when" at the beginning of phrases, and the k sound is suggestive of the qu- beginnings of similar words in French and Spanish, or the ch- of Italian. On the other hand, the way they're used is more closely parallel to the German "was/dass" and "Wenn". In the sentence, "He understood what the problem was," English tends to parse "what the problem was" as an implicitly compound object of the verb "understood", and hence we consider that utterance to be one phrase. In German, compound objects like that are considered to be subordinate clauses of their own -- it comes out more like "Er verstand, was das Problem war," which is puncutated like two related phrases rather than one. The phrasing of whatever the subtitles are written in uses a lot of commas to set "ki" and "ko" phrases off from the rest of the sentence, making the structure and rhythm closer to German. The combination suggests that the language is from the southern or southwest-ish end of the Slavic languages, where there would have been a lot of regional influence from things like Austrian German and Italian.

There are a fair number of cognates, which I would expect in a documentary on medical conditions, as most medical nomenclature comes from the Latin, as dragged kicking and screaming through English. There are a few less technical cognates, such as "levo" for "left" and "oko" for "eye", but generally they are attached to such fundamental things -- like directions and body parts -- that it's equally likely that they stem from a common ancestor in some stage of proto-Indo-European language development. "Love" seems to be something that starts with "lj-", which is vaguely Russian-y, but "life" is some near-vowelless mess that starts with Z-caron, and bears no resemblance whatsoever to that word in any other language I know.

Some of the negations are weird. Sometimes the negatory particle is a free-floating "ni" or "ne" and seems to come before the verb, but there are standard forms like "nisem hotel-", which appear to be various tenses of "(I) do not want", and "nisem videl-", which appear to be various tenses of "(I) do not know".

Anybody happen to know what the hell this is? Bunging a few phrases through Google Translate in an investigatory fashion results in guesses in the general Croatian/Slovak/Slovenian region, but everything in that area is so similar that a lot of it would have not-quite-identical valid translations from more than one language.