I have found all of the planned Duolingo languages using a simple trick

[oscart182]

http://incubator.duolingo.com/courses/en/af/status

I will be using Afrikaans as an example. As you can see in the following URL, "af" represents Afrikaans.

http://incubator.duolingo.com/courses/en/af/status

The full list of two-letter language codes can be found here: https://en.wikipedia.org/wiki/List_of_ISO_639-1_codes under the 639-1 column.

These are the ones that worked when I typed them in:

Afrikaans
Albanian
Armenian
Azeri
Bengali
Bulgarian
Catalan
Croatian
Czech
Estonian
Finnish
Galician
Georgian
Gujarati
Hebrew
Icelandic
Kannada
Kazakh
Kyrgyz
Lithuanian
Latvian
Macedonian
Malay
Marathi
Mongolian
Punjabi
Persian/Farsi
Serbian
Slovak
Slovenian
Swahili
Tamil
Telugu
Urdu
Uzbek

I believe I have everything, but feel free to tell me if I missed something.

Edit: there is also Sindarin, Dutch (Belgium), Klingon, and Chinese (Traditional)! Thanks, davidvdb

Edit: I also found Dothraki by looking in the source code for the Incubator.

Edit: Here is the source code:
duo.language_names = ['Greek', 'Esperanto', 'English', 'Swedish (Sweden)', 'Lolcat', 'Afrikaans', 'Swahili', 'Catalan', 'Chinese (Cantonese)', 'Gujarati', 'Swedish', 'Zombie', 'Czech', 'Arabic', 'Ukrainian', 'Irish', 'Basque', 'Estonian', 'Chinese (Traditional)', 'Azeri', 'English (Pirate)', 'Spanish', 'Chinese', 'Russian', 'Galician', 'Norwegian (Nynorsk)', 'Norwegian', 'Norwegian (Bokm\xc3\xa5l)', 'Turkish', 'Indonesian', 'Latvian', 'Lithuanian', 'Punjabi', 'Thai', 'Vietnamese', 'Italian', 'Hebrew', 'Icelandic', 'Polish', 'Tamil', 'Dutch (Netherlands)', 'Belarusian', 'French', 'Bulgarian', 'Dothraki', 'Telugu', 'Slovenian', 'Croatian', 'Bengali', 'German', 'Dutch (Belgium)', 'Danish', 'Farsi', 'Uzbek', 'Hindi', 'Finnish', 'Armenian', 'Hungarian', 'Urdu', 'Japanese', 'Faroese', 'Georgian', 'Romanian', 'Portuguese', 'Malay (Brunei)', 'Kazakh', 'Albanian', 'Mongolian', 'Korean', 'Kannada', 'Macedonian', 'Klingon', 'Slovak', 'Malay (Malaysia)', 'Tatar', 'Sindarin', 'Malay', 'Marathi', 'Kyrgyz', 'Swedish (Finland)'];

[writchie4]

Another user did something similar a few months ago: https://www.duolingo.com/comment/4532113

It's interesting that you got a different set of languages than they did.

[_pinkodoug_]

And to expand a bit on what I pointed out in that thread, most of these are just automatically generated based on the language code combinations that they've accounted for in their code / routing rules for their framework. They're basically place holders, and are not necessarily indicative of any immediate plans to begin work on those courses.

cGlua29kb3Vn

[_pinkodoug_]

Also, it's worth noting since that post over 4 months ago, Duolingo has added 2 "source languages" (as I described them in that post) and 1 additional "target language" for each. This brings the number of combinations to 1760 from the 1580 mentioned previously. I should also mention that the target languages list also contains the source language as well as some jokes (zombie, lolcat and pirate), so in reality there are only 76 targets per source so only 1672 of those are legitimately possible future courses.

[oscart182]

I doubt they are automatically generated because were many language codes that did not work when I typed them in. They must have hand picked them from a list.

[KansasBurri]

Maybe they've added or are planning to add more than they did in the comment you mentioned?

[StrapsOption]

No Maltese. I doubt this means anything, I mean look at this: http://incubator.duolingo.com/courses/en/en/status .

[oscart182]

Lol. That's hilarious, why does the system even allow that?

[StrapsOption]

I don't get it.

[oscart182]

English for English speakers. You linked it in the first post on this comment chain. http://incubator.duolingo.com/courses/en/en/status

[StrapsOption]

No sorry, I meant I don't get why it's even there.

[Eikoopmit]

I'm considering applying for that one...

[Ontalor]

Well, really they want to eventually teach ALL languages, so that's probably just what they've coded or what people have applied to teach so far.

[oscart182]

Am I the only one excited for the Afrikaans reverse course...if that will ever exist? :P

[mjacobsen121]

Nope. This looks awesome!

[pskully]

I'd be quite happy if there were ever a Slovenian course. I wish my Slovenian was to the level that I could apply to contribute.

[qwertylaal]

If they do all 7,000 languages (assuming the number does not go down) we will get 49,000,000 combinations. That WILL be fun.

[davidvdb]

Try sjn, tlh, zh-TW, and nl-BE. :) And this one will be very useful, if the elves will ever get out of Middle Earth. :)

[oscart182]

Thanks!

[Drakessis]

Lolcat? I speak that!

[Drakessis]

Lolcat? I speak that!

[jimnicholson]

Instead of giving you a 404 error - they are giving you a nice message. It doesn't mean anything, other than that there is a defined list of languages. They display the message for any combination of these languages. Meaningless. It is probably exactly the same list they use of the volunteering page.

[Tattamin]

Wohooooo - errr, I mean: Arrrr, I wanna learn English(Pirate)!