Serbian doesn't just stress syllables - it pitches them
The A1 pronunciation lesson mentions, in one sentence, that standard Serbian technically runs on a pitch-accent system before setting it aside as too advanced for beginners. It is one of the more surprising facts a new learner can hear about the language: Serbian marks not just where a word is stressed, but how - rising or falling, long or short - the same four-way system found in Swedish, Japanese and Ancient Greek, and almost nowhere else in Slavic.
Buried in the pronunciation lesson linked below is a single sentence that most beginners skim straight past: standard Serbian technically has a pitch-accent system with long and short syllables - a genuinely advanced topic. Then the lesson moves on to three practical rules and never returns to it. That sentence is worth coming back to, because the thing it is quietly setting aside is one of Serbian's genuinely rare features on the world stage.
Four accents, not one
Standard Serbian (and Croatian and Bosnian, which share the same accent system inherited from a common ancestor) distinguishes four pitch accents on a stressed syllable, crossing two independent choices: the pitch can rise or fall, and the syllable can be long or short. Linguists name them accordingly - short-falling, long-falling, short-rising and long-rising - and the same three-syllable word can, in principle, carry any of the four depending on both. Russian stress makes only one of these choices, which syllable, and marks neither pitch direction nor length at all; English is the same. A Serbian dictionary that wants to be complete has to mark all of it, which is exactly why the everyday spelling you read on a street sign does not bother.
Rare company
Pitch accent of this kind - where the same stressed syllable can carry different melodic contours without changing which letters are written - is uncommon enough worldwide that linguistics textbooks reach for the same handful of examples every time: Swedish and Norwegian among the Germanic languages, Japanese, and the reconstructed accent of Ancient Greek and Vedic Sanskrit. Serbian's closest relative in this respect is Slovene, which has a broadly similar system, and, more distantly, Lithuanian, a Baltic language whose pitch accent is often cited alongside Serbian's as evidence that both descend from a very old, shared Indo-European feature. Most of the Slavic family - Russian very much included - simplified this system away centuries ago, keeping only the plain stress.
None of this is a reason to worry at A1, or even at B1. Getting the pitch direction wrong on a word rarely changes its meaning - the rule that stress never falls on the last syllable, from the pronunciation lesson, already does most of the practical work a beginner needs, and a foreign accent that gets the syllable right but the melody flat is still completely understood. Pitch accent matters for sounding native, and for the small number of words where it is the only thing distinguishing two different meanings - it does not matter for being understood.
Where it actually shows up in a learner's ear
The most common place a learner notices pitch accent, usually without having a name for it, is the difference between a longer, more melodic-sounding syllable and a shorter, flatter one on words that otherwise look identical in writing - vowel length is not marked in ordinary spelling, only in dictionaries and some textbooks, using a small mark over the vowel. That silence in the spelling is itself informative: it confirms that Serbian orthography, so exact about consonants, made a deliberate choice not to chase this one down to the letter.
Biblioteka je otvorena do devet.
The library is open until nine.
Same word as the pronunciation lesson's own example - third-syllable stress, and its pitch contour is never shown in this spelling.