Some diacritics and special characters (like ligatures) are accepted in Contemporary English: https://en.wikipedia.org/wiki/English_terms_with_diacritical_marks

Examples of English spellings: coöperative, reëlect, naïve, soupçon, frappé, piñata, Geiger–Müller, Wilhelm Röntgen, László Bíró, …

Some others aren't accepted and wouldn't be used in any publication for an English spelling.

Examples of characters never used in English words: ⱥ, Ω, あ, …

What are the lists of characters with diacritics or special characters (like ligatures) accepted in Contemporary English words?

Question is narrowed to reference organisms or major publications, as:

  • Dictionaries
  • Universities, Academic publications
  • Newspapers

Question does not include:

  • anything non-Contemporary, i.e. older than October 6, 1960 (American Standards Association's first meeting to create ASCII)
  • non Latin/Roman characters, as you would perform romanization on it to make it an English spelling
  • symbols (Ƭ̵̬̊) or emojis (😂, Oxford Dictionaries 2015 Word of the year)
  • fiction publications, blogs

Example possible partial list of accepted characters based on Wikipedia article above, would be (in lowercase mostly): äëïöüáóíéèàìôēāăŏčšřžåçșñďľňťŁđćĦ

  • It depends on the publisher. There is no official list, as there is no single definition of standard English.
    – herisson
    Nov 21 '16 at 4:02
  • 2
  • You don't get to pick and choose how to write somebody else’s name. If it’s written in the thing we have come to call the Latin alphabet, then you have to write it the way they tell you to. It doesn’t matter if it as letters we don't use in English. If you don’t believe me, then Hafþór Júlíus Björnsson might care to have a word with you. Please see this related question, especially the excerpt from Bringhurst.
    – tchrist
    Nov 21 '16 at 4:11
  • 1
    This is arbitrary and differs according to domain. For instance, though you say 'Examples of characters never used in English: ⱥ, Ω, ...', Ω is often used in English science textbooks. Also, an illustation could contain any symbol. Nov 21 '16 at 10:29
  • 1
    @tchrist, I think it's worth to put Robert Bringhurst's opinion as an answer instead of just a comment.
    – Cœur
    Nov 23 '16 at 5:15