"Speaking" - being able to express any of your thoughts with sufficiently many words while applying the language's grammar correctly.
I don't know how to create polls with the possibility to select >1 answer, so it's a bounty instead (which is also possibly more fun);
Instead of voting, write the name of the language in BOLD CAPS (if you're the first one to mention it) and write a > 10-word original text in it with a translation provided, so that others can check if it's correct. After confirmation of grammatical correctness and sufficient meaning (repeating one word 11 times doesn't count), most likely by me, I will award a 100-700 mana bounty, depending on the text's impressiveness (inherently lower for Toki Pona, etc.).
If someone has mentioned a language you speak, you won't necessarily get a lower bounty (if you don't copy their text, that is), just write your message as a reply to the first mention of your language.
I got introduced to EA/rationality at an Esperantist event, so there is at least a minor overlap in that regard and with the creation of Mini, maybe there will come a resurgence of other conlangs (Lojban has/had some fans on LessWrong for example).
Related questions
Sure, I'll do LOJBAN.
.i do djica tu'a loi ckafi poi se ba'o nenri loi sakta goi sy. ji loi tcati noi claxu sy.
Idiomatic English: "Do you want the coffee, which already has sugar in it, or the tea, which doesn't?"
Literal morphemic translation: {(new/separate sentence) you want something-about mass-of coffee (start restrictive relative clause) (swap x1, x2 of following selbri) PERF contain sugar (anaphora marker: bind previous sumti to: "S") (QUESTION: supply appropriate logical connective) mass-of tea (start non-restrictive relative clause) lack S}
Note that unlike the corresponding English question, an answer in Lojban consists entirely of supplying that missing connective, so entirely acceptable Lojbanic answers include "neither" (na.enai), "both" (.e), "exactly one but I'm not telling you which" (.onai AND na.o), "bring me both or don't bother at all" (.o), "bring me tea if you feel like it but don't forget the coffee!" (.u), and "both mixed together" (joi)!
example - TOKI PONA:
mi wile jo e mani mana mute tan ni: mi ken pana e ona tawa kulupu pona wawa.
Literal translation: "I want to have a lot of mana money, because of the following reason: So that I can give it to strong good groups [effective charities]".
Free translation (optional): "I want to have a lot of mana so that I can donate it to effective charities"