How do i get spell checking for my language in libreoffice?

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You need to install libreoffice-langpack-"your language", for a list of all available languages, run:

dnf search libreoffice-langpack

to install a language pack, run: (in this example dutch)

sudo dnf install libreoffice-langpack-nl

After doing this, you can go to tools -> language -> For All Text -> more, then click on the dropdown next to Western: in the Default Languages for Documents section. There you can now select your language (dutch in my case). If you want the default spellchecker language to be dutch, also uncheck for the current document only.