Excited to see Japaneses and Vietnamese on this app but I've been using Doulingo for some time to learn European centric languages and the Asian languages have mostly been ignored. Why? and when can we start to see more of these languages offered, such as Tagalog?
Because many of the Asian languages have a different type of script (Chinese, Japanese, Thai, etc.). These types of languages are very difficult to create a course for because they'll need to teach a person the script as well as everything else. This is likely the reason that it has taken Duolingo awhile to introduce these languages (also keep in mind that these contributors are creating courses for free).
With the release for Vietnamese and Japanese [for English Speakers] and the soon-to-come Korean course, it shows good potential for other Asian languages. Chinese for English Speakers will most likely be introduced soon in the near future, according to the CEO of Duolingo.
I know about the scripts and everything, but doesn't Hebrew also have a different script and that was released. Im not being rude or anything by the way I love duolingo I'm just using an example. Though I agree that they should find a way to actually teach the script because Hebrew course is hard to complete given they don't teach the script.
Going by what Duolingo offers, I would say the order from easiest to hardest is:
Latin alphabet -> other alphabet/abjad (like Hebrew) -> syllabary (Hindi) -> connected alphabet/abjad (Arabic) -> logogram (Japanese)
Centric European languges? You have Guarani, Welsh, Irish, Russian, Ukrainian, Swahili, Turkish and Hebrew.
Hebrew is Asian. Russian and Turkish are spoken in countries which are mainly Asian. Furthermore there are several languages with fewer native speakers or less commonly learned languages like Hungarian, Catalan, Romanian, Polish and Esperanto. Indonesian (Asian), Korean (Asian), Hindi (Asian) have been mentioned. Yiddish (European) and Haitian Creole (Indo European - Romance from the Caribbean) are in the incubator. Those successes should not be ignored either. Give it time.
English for Thai speakers is in beta now. English for Telugu, Panjabi and Tamil speakers is in the incubator. Usually they finish these courses first and then they create a course for English speakers, often not the other way round. So there is hope for these as well.
In my opinion Duolingo should also include South, Central and North American languages as well as African languages. But European languages were the point to start for Duolingo. I see nothing wrong with it. (I'm European by the way.)
Because of limitations, Duo worked on their system for many months before they were able to start building a Japanese course inside the incubator. The founder of Duolingo said today in an AMA that he hopes to see Chinese on here by the end of this year (I don't know if he means in the incubator or as a completed course), now that many of these limitations have been overcome.
Korean, Hindi and Indonesian are 3 major Asian languages currently in the incubator for English speakers, so I wouldn't say Asian languages are being ignored, they're just on their way.
Portuguese is also spoken in Asia (Macao and East Timor). The Portuguese on Duolingo is Brazilian, the Spanish is Latin American).
https://en.wikipedia.org/wiki/Languages_of_Asia (not even close to complete - also here are the most common languages although the list is a little larger than usually considered) is also a nice overview. Maybe Duolingo should keep focusing on the less commonly learned languages as well. It's great to have Chinese, Tagalog, Japanese, Indonesian, Hindi and Korean here. But there are many more interesting languages that are taught nowhere or very rarely. Some of them are endangered.