What languages are currently supported?
Are there plan to support more languages in the future?
Monero does support arbitrary language seeds.
Currently, several languages are implemented in terms of seed: English, Italian, German, Spanish, Portuguese, Japanese, Russian. More may be added by people familiar with other languages, as the main task is to find a set of 1626 words in a language which obey a few simple rules:
That last requirement bears some explanations: the intent is that a mnemonic seed only needs the first few letters to be unambiguously recognized as a word for that language's list. For instance, the English word list has a 3 letter unique prefix, which means that if a word starts with "pig", there is no other word in the list which starts with that same 3 letters prefix. Here, the only word starting with "pig" is pigment. Pig would also work, since only the prefix matters. This allows one to change words in order to remember better, as well as potentially disguise a mnemonic seed by using words that do not appear in the list, but which share a prefix with one of those words.
As far as I know, there are no new languages currently slated for inclusion, but those simple rules are there for anyone who wants to have their own language included.
Update: in May 2018 (version 0.12), mnemonic seeds are available in the following languages:
For example, if the user selects Dansk (Danish) as the language used in the wallet, English will be the language of their mnemonic seed, because there's no Danish word list yet.
The Dutch, English, Esperanto, French, Italian and Portuguese word lists do not contain any diacritics. I'm not sure how all the word lists were created, but I happen to know only words written with diacritics were selected for Esperanto, in order to make it easy to input the correct words on any device. And for Portuguese, diacritics were simply left out in words where they would normally be used.
First off, yes, there are multiple languages available.
At this point I am aware of English, Japanese, and Spanish as options.
I believe so, though which ones exactly is likely still up for debate.
An easy way to see various language seed options is to visit https://moneroaddress.org/
Look at the source code spoken_language_name.h files here where you can see the actual seed words for different languages.