Problem. Spell-checker in Calc does not work at all, because I cannot set the spell-check language.
In LibreOffice Writer, when you click Tools → Language you should see a submenu called “For All Text.” Under this menu you can set the spell checker language “for all text” to “English (USA),” so that spell check will work.
However, in my version of Calc (126.96.36.199, on Windows 8.1 at least), there is a bug preventing this from happening. The “For All Text” submenu does not exist. Assuming you have the spell-check dictionaries installed, there is a work-around.