title_body: What features make a language easier to learn for people learning it as a second language? This question is different than the previous one titled “Which features make a language easier to learn?” in that I'm not interested in making it easy for L1 learners. For them learning the language spoken by their society is an inevitability.
  
  Specifically, I'm interested in making a language that is objectively as easy to learn as possible for people learning it as a second language. And these features should help people regardless of what language they speak natively. 
  
  It seems intuitive that there would exist features that would help to create that.
  
  For example, take French or German and remove the genders. This seems like it should make the languages easier to learn without losing any communicative power. Another example would be phonology. If English were to remove the 'th' sound it would be easier for speakers of other languages to learn.
  
  I also realize that it may be the case that there just isn’t enough research on this topic to know definitively what features are best for this.
upvoted_answer: It depends very much who your target audience is.
  
  It is easier to learn languages that are similar to your own; as a German speaker, learning English is not that hard, apart from the grammatical features (aspect, for example) that don't really have a German equivalent. It's mainly a matter of learning the huge vocabulary with all its not-quite-but-almost synonyms.
  
  Same with Esperanto. Grammar is easy, and most of the vocab is not too hard either. Here it's the particles which are the tricky bit.
  
  I'm currently learning Dutch and Swedish, which are both similar to German, in some respects. No big deal. But both Arabic and Korean are a lot harder, and I gave up on Russian. These languages are very different from German, and thus harder for me to learn (the different alphabet is not the issue).
  
  Klingon is hard for me to learn, because it has a different sentence structure (OVS, as opposed to SVO). If my native language had OVS as well, for example Apalaí or Hixkaryana, I think I would find Klingon much easier. Especially since Apalaí is also agglutinative, like Klingon.
  
  There is a list of languages ordered by difficulty (from the Foreign Service Institute). The 'easy' languages are all Indo-European, and the hard ones are Asian/Semitic. You can imagine that the same list produced by a Chinese or Japanese institution would look very different.
  
  Languages have no 'absolute' difficulty, but only relative. So to answer your question, you can make a language easier to learn for people if you make it more similar to their L1. Which, I guess, is the reason why there is no universal 'easy' language that we all speak...