How is Sigil to know a word is in British and not American?
If the main language is set to US, individual phrases in British must be clearly marked:
Code:
<span xml:lang="en-GB">colour</span>
Maybe it seems difficult, but if I have a whole book in Polish, and only a few dialogues in French, Italian or Spanish, it is obvious for me to mark the correct languages in these specific places. Then not only the spell check in Sigil works correctly, but also – what is equally important – appropriate readers can distinguish the language and for visually impaired people such expressions are read in correct languages by correct voices, and additionally words in foreign languages are hyphenated according to dictionaries assigned to these languages, not the main language in the e-book.