The software, which is not worked on, dies. So the piece of software is never finished - till it dies.
That said I would like to inform you that I've actually done it. There is a piece of software which brings multi language spell check to Sigil, with, as far as I can see, all previous functionality and some more. Not perfect because perfection comes with experience.
Will Sigil have it? I think not. Not in this form.
Let us be honest. Almost nobody really needs it: seems to be my specialty in Sigil features

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The devs have much more important thighs to do: implementing epub 3 and some more.
And I'm in a middle of an personal circumstances that will make my further work on Sigil impossible - I think... at the moment... Christmas coming...
If anybody really needs it - it is relatively easy to find. With every passing day it dies of course...
The good news: last time I've checked the Calibre Editor parsed Multilanguage01.epub correctly: it was not the case when I've first checked... haven't said anything, because I knew Kovid will get it right as soon as he noticed

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