How many Indigenous Australian languages are there? How similar are they?

At the time of European invasion *cough* settlement, the guesstimate is 200. The guesstimate is based on poor data, since many were wiped out so quickly, and on Lexicostatistics — because we don’t have enough data to make a good linguistic assessment of what counts as a different language otherwise.

We could of course ask the indigenous Australians themselves how many languages there were. Their answer will be closer to 600, which was the number of distinct tribes — because like people everywhere else, their notion of what counted as a distinct language was based on identity politics rather than mutual intelligibility. (I see that Wikipedia is now using the identity politics answer rather than the white linguists’ answer: Australian Aboriginal languages ).

That’s a distinct answer from how many languages are alive today, being passed on to new speakers, and not revived from written sources after going extinct. That answer is closer to a dozen or so.

How similar are they? Tasmanian is very poorly  attested (likely nine distinct languages jumbled up in a concentration camp), but we are pretty sure they have no detectable relation to the mainland languages. The bottom 2/3 of the mainland belong to the Pama–Nyungan languages, meaning they have discernable similarities. Given that pana means “man” in one end of the family and nyunga means “man” in the other end, they aren’t that similar. The guesstimate is that they are of a similar time-depth as Indo-European, 5000 years.

The top 1/3 of the mainland are heterogeneous, and are  not particularly close to each other; it doesn’t seem to have been definitively proven that they are related to Pama-Nyungan, either.

Could emojis ever replace written language? Why or why not?

If you want emojis to be not just a bunch of nouns, but the basis of a full written language, with verbs and prepositions and pronouns—then you’re going to need to supplement emojis with some sort of grammatical sign system. They will end up looking a lot more like Blissymbols.

Where can I read Ancient Greek texts?

Perseus, as Philip Newton said.

The TLG – Home (my employer) has pretty much all the Ancient and much of the mediaeval corpus available by subscription, with a subset publicly accessible.

The Little Sailing (Ancient Greek Texts) has older editions of many texts.

As always, a lot of old editions are available on Google Books and (Digital Library of Free Books, Movies, Music & Wayback Machine).

Was the Byzantine Empire in the Greek medieval state?

Yes and no, but in a different way from Andrew Baird’s answer.

The lingua franca and administrative language was Greek. The Empire called itself Roman, but its scholars knew a lot about Ancient Greek and very little about Rome. The core of the Empire was Asia Minor, much of which was Greek-speaking until the Turkish invasions, and Greece.

But at least until the Fourth Crusade, the Empire was bigger than Asia Minor and Greece, and its ethnicities matched—whatever language they may have used in writing and the church. A large number of its emperors and officials were ethnic Armenians, and had the surnames to match (Category:Armenian Byzantine emperors, e.g. John I Tzimiskes). The scholar John Tzetzes was proud of his Georgian heritage. John Koukouzelis, who  reformed Byzantine chant, was most likely Bulgarian.

I have a cousin with an Arvanitika surname, Tzathas. When she went to uni, her prof commented how her surname sounded “Byzantine”. And it would indeed sound Byzantine, since that was when half the surnames of famous people weren’t Hellenic.

Byzantines resented Westerners calling them the Greek Empire instead of the Roman Empire—not only because it denied them continuity with the Roman Empire, but also because Byzantium wasn’t confined to Greece. Of course, Byzantines, and their successor state the Ottomans, were profoundly indifferent to ethnicity anyway, which is why the non-Hellenic background of Byzantines was not paid much attention. What mattered was religion; which is why the Ottoman Rum Millet and the Modern Greek use of Romioi (Names of the Greeks ) primarily referred not to ethnic Greek, but to Orthodox Christians.

How did the future tense appear in Latin?

The future -b-, and for that matter the imperfect -b-, come from the Indo-European verb for “be”, bhu: The Latin Language. So amabo originally meant “I am to love”, and amabam “I was to love”. The process of words turning into grammatical affixes is called Grammaticalization. And one of the characteristics of grammaticalisation is that it happens over and over, in the same language: French aimerai involves the same process as amabo, but with the verb for “have” rather than “be”.

What makes Modern Greek an interesting language to learn, from a purely linguistic point of view?

  • The consequences of diglossia, which persist even if diglossia itself does not—including the trainwreck of Modern Greek phonology from all the spelling pronunciations from Ancient Greek, the lexical and morphological doublets, and the all-round linguistic insecurity.
  • The survival of archaisms in Indo-European, including the middle voice (semantically), the vocative, and the three genders
  • As Joachim said, the survivals and reorientations from Ancient Greek. I’ve often been curious what Modern Greek looks like to classicists; the best answer I’ve heard is “drunk”.
  • The dialectal diversity (though Greek is hardly unique in that.)

What are the origins of the inhabitants of Mani in Greece – are they Spartan?

Agree with George Bekas, and one should always be wary of claims of genetic purity. But we do know anecdotally that:

  • Its major town Gythium was a Spartan port
  • They were very late converts to Christianity (10th century: Nikon the Metanoeite)
  • Mani was a no-go area for certainly the Ottomans, and likely earlier invaders—so it’s certainly possible that they have more Ancient Greek DNA (ugh) than their neighbours. We do know that there were Slavic settlements to the north of Mani (Melingoi, Ezeritai), and that Slavonic was still spoken in the area in the 15th century (John Cananus)
  • They speak an archaic dialect of Modern Greek [Maniots]—although not one with notable Doric lineage (unlike the Tsakonian language)
  • They have contempt for the inhabitants of the neighbouring lowlands, calling them Vlachs. A couple of rich ironies about this:
  • 1. Elsewhere in Greece, Vlachs refers originally to Aromanians, and in colloquial usage, is equivalent to hillbilly—referring to highlanders, not lowlanders.
  • 2. When the Maniots settled in Corsica (Cargèse), Vlachs is what they called the surrounding Corsicans. Who at least did speak a Romance language.

How do you translate “Freedom means choosing your burden.” (in the correct grammar) in Greek language? And in Greek writing as well?

Tough, because it’s got to be idiomatic.

In Modern Greek: You have the choice of the formal ελευθερία or the colloquial λευτεριά. We’ll go colloquial, it has more resonances.
Burden: φορτίο is formal. Γομάρι is colloquial, but it also has ended up meaning beast of burden, hence jackass, so it won’t do. Unless you have religious objections, the culturally appropriate equivalent is probably “your cross” (to carry). So:

Λευτεριά είναι να διαλέγεις το σταυρό σου.

or maybe, spelling out “to carry”:

Λευτεριά είναι να διαλέγεις το σταυρό που θα κουβαλάς.

Yes, everything is longer in Greek.

Are speakers of present-day Volapük generally able to read texts in the original Schleyerian Volapük?

I don’t know the answer, but I will point out something the OP is aware of, but others may not. Like many artificial languages, Volapük underwent significant reform in 1931. I don’t know to what extent Volapük Nulik and Volapük Rigik are mutually intelligible, but if they aren’t, that’s just yet another instance of artificial language reform—and not that interesting to students of artificial languages. It’s the unplanned shifts in artificial languages, I’d argue, that are unexpected and interesting.

What is the most minimal language?

Artificial languages are where you’d look of course, and there are much simpler languages than Esperanto. Basic English was renowned for having a small vocab. My own favourite, with a comparably small vocab and a much tighter grammar, is Interglossa (as opposed to its revival Glosa).

Natural semantic metalanguage has an extremely small number of concepts, but is parasitic on natural language grammar, and is not meant for communication but for definitions. So it’s not quite the same thing.