Hi!
I’m aware that that Finnish is a small language, but I’d more happy to recommend this to my friends and colleagues if this minor oversight was fixed. Otherwise I like the approach you have with combining the text editing and the process of it. 
Br,
Timo
It seems you can install your own. If you go to the appropriate Windows forums, you’ll find threads explaining how to do so. If you can’t find any, just post a new thread asking how to install a Finnish dictionary. I’m a Mac user, but I know Windows 1.9.x uses Aspell, While the v. 3 betas/release candidates use Hunspell.
Good luck
Mark
A bit old thread, sorry to “bump it up”, but since I found this thread myself and resolved the problem on Windows Scrivener 3 (hunspell) - both by modifying my workflow and with some hacking - , I’ll share what I’ve done:
Finnish language support development for hunspell has been dropped due to its unsuitability to Finnish language since 2012 but there is a project called Voikko which provides more suitable dictionaries and both spell checking and grammar libraries. Scrivener does not support Voikko.
Or the other way around, Voikko does not support Scrivener, which would be impossible anyway, because Scrivener does not publish an editor API or provide a plug-in interface for third party developers but only file system structure. A file-based approach can be used indirectly with Voikko, but only off-line from Scrivener’s file system:
I use Voikko with Scrivener projects in a workflow where I sync the text files in .rtf-format to a filesystem external to Scrivener, edit them for corrections with LibreOffice Writer which Voikko is supporting. Likewise, with French text I do the same with the excellent Antidote 10 (non-free) suite. With LibreOffice Writer in my workflow, I can do both Finnish and French with convenient grammar tools and then syncing the corrected files back to Scrivener.
To get the instant Finnish spellcheck working, there are some hunspell fi_FI packages still available from older Linux distro packaging, it is enough to browse the APT- archives. The problem is that since Scrivener does not list fi_FI as language you cannot add those files as they are, even if they are otherwise system architecture independent text files. Maybe this thread will encourage Scrivener to take into account also the Finnish language dictionaries. While waiting for that, you can trick Scrivener: It does not recognize Finland but it recognizes its southern neighbor Estonia. I select in Scrivener for download the dictionary Estonian (Estonia-et-ee) and check that it works when selected as a spellchecking dictionary.
The following brute force technique would likely work with any language so if you want to keep Estonian and want to have also the Finnish spell-checker, just pick up some other dictionary as a victim.
Estonian-et-ee_as_fi_fi.zip (892.4 KB)
# use your Explorer right-click to unzip. Here is the checksum of the above archive
C:\Program Files\Scrivener3\hunspell\dict>certUtil -hashfile Estonian-et-ee_as_fi_fi.zip SHA256
SHA256 hash of Estonian-et-ee_as_fi_fi.zip:
57cbd7d84ef27618d7e6d9daddf4ea3fff6a4cd8cb2b4aaa0b300ed9820606d5
Test:
