Orginally, Esperanto was called "la internacia lingvo" (the International language), but people used the pseudonym of the author as the name of the language, which is why esperanto means "someone who hopes" and Esperanto with a capital is the name of the language.
Latin in Esperanto is either Latino or la latina lingvo
Well, it does actually still make sense - the meaning of the sentence is arguably the same, whether or not the definite article is used.
However, as the lessons have gone on, it is clear that using the definite article before a language name (la angla, la franca, la germana, etc) is a feature of Esperanto.
And the definite article is not used for the Esperanto language unlike with other languages - instead the word Esperanto is capitalized (in Esperanto), whereas other language names are not.
I would point this out as one of the strange irregularities in an otherwise logical language, but it's really not the language's fault that it's irregular like that. Esperanto wasn't even supposed to be the name of the language, it's just the name Zamenhof used for the author, instead of his own name, when he published the first book about Esperanto. He wanted to remain anonymous, I think because he didn't want it to matter who came up with the language. People called it "Esperanto's Language", and it eventually just became "Esperanto". It's too late to make it consistent now, I guess. It's kind of ironic, though.
It's never too late to fix a mistake. And this is, at a very fundamental level, a horrible mistake.
Not because it's inconsistent (it is), but because it's arrogant and tone-deaf. There's nothing like saying "Your native language isn't good enough to deserve a capital letter, only my language deserves it" to annoy people...and it doesn't take much annoyance to get the casual learner to drop learning.
And, what's worse, the people who have knee-jerk reactions to things like this are the people who most need to have their horizons expanded.
Now, there's not a lot DuoLingo can do about issues like this. The owl's job is to teach a language, warts and all. And, when learning a language, you should learn the warts. But, once you've mastered a language, then you can decide for yourself whether you still want the wart or if you'll work around it.
It's never too late to fix a mistake.
Heh. Would there were more Esperantists who thought like this. Most of them acknowledge the mistakes and say we can't do anything about them, because that would put a crack in the language. If we fixed every mistake we came across, that would just fracture the Esperanto user base into a bunch of different pieces, which would defeat the goal of a worldwide language before it had even really begun. I know where they're coming from. My goal is for Esperanto to be the penultimate language. Once everyone knows Esperanto, and it's accepted as the international auxiliary language, then it can be reformed, officially, by professionals. And the changes would be such that it would cease to be Esperanto. My hope is it'll resemble Ido to a large degree, because Ido was created by a committee, some of whom were linguists, most of whom were scientists, as a reformation of Esperanto to better suit the most people, and the scientific community. Unfortunately, it tore the community apart.
It might happen like that in the future, but I hope not. This is assuming of course that English doesn't become the de facto international language, which it very well might.
The reason for this difference is mentioned in the notes. Natural languages use an article and aren't capitalized because they're adjectives, i.e. "la angla" is short for "la angla lingvo"; planned and dead languages usually end in '-o' and don't use an article - my guess is this irregularity was caused by, as Wilcynic mentioned, people starting to call Zamehof's language "Esperanto".
Kinda strange, but the distinction is interesting.
So, when using adjectives substantively, does one always leave them in adjectival form? Would anglo then be an Englishman? This sounds an odd feature of Esperanto that makes adjectives less versatile, rather than more. Why would one not simply use a nominal ending on the adjective to make it a substantive?
Now you have exactly hit upon the real reason. "anglo" is an Englishman which is why it cannot be the name of the language. This is what happens when there are many nouns that can be made from an adjective, then you may have to specify which noun is involved: "La angla lingvo" but then the word for language became dropped so "La angla" is the language. With dead or constructed languages, you don't have a country that has citizens to be talked about so the main noun "Esperanto" or "Latino" can be used for the language.
In that case, how does Esperanto handle language names that aren't used as nationality descriptors? For example, Yiddish appears to become jida.
Yiddish is a live language not a dead one. It grows and changes with the people who use it unlike the dead languages and the constructed languages. They set up the cut off as being for constructed and dead languages, so it slips through the cracks of their system, I suppose. There are other languages like that I am sure. So, my theory does not stand the test of time and there are people who speak Esperanto and they call them "esperantistoj", so they could have worked out a different system that was the same for all languages, but they didn't. Do you think that they simply don't consider dead or constructed languages to be actual languages to be used with the word "lingvo"? or Do they set dead languages and constructed languages apart because they are not supposed to change? I think the origin of Esperanto being capitalized has to do with the first book "Dr. Esperanto's International Language" . People started calling the language Esperanto from the pseudonym of Zamenhof.
Not exactly, Latin is also capitalized out of respect for dead languages. Constructed languages are also capitalized, because they are not considered living languages. They are set up and expected not to change. I wonder what would happen if one of the constructed languages became used everywhere and started to stray from its construction to grow and change and become alive?
Greek is not capitalized in this dictionary. Although it was a root language, it has continued to change and be used: la lingua greca. https://www.duolingo.com/skill/eo/Languages
http://reta-vortaro.de/revo/ (Click on top left tab marked Lingvoj)
http://www.gutenberg.org/files/16967/16967-h/16967-h.htm#letterL You are right that this dictionary also shows "Greek" as "Greko". http://www.gutenberg.org/files/16967/16967-h/16967-h.htm#letterG Perhaps with the Capital letter and the -o ending, the word differentiates Ancient Greek from Modern Greek which would be "la lingua greca"?