Created attachment 122000 [details]
Spell-check work-around and bug--see paragraph 2
Spell check in Calc does not work *at all* (without a special work-around), simply because one cannot set the spell-check language! I marked this item as "critical" because it prevents Calc from being used in a professional environment, where spell-check is a must-have.
Finding the work-around has taken me about 5 hrs of research time. Most people would give up long before then.
In Writer, I can go to Tools --> Language --> For all text --> English (USA), and spell-check works fine, now that I have selected the language.
In Calc, however, this option does not exist. I cannot set the language at all via the Tools --> Language menu, as the "For all text" submenu is nonexistent.
Highlight all cells (ctrl + a) → right click → Format Cells → Font → set “Western Text Font” to the language you want to use for spell-check, ex: “English (USA).” Now that you have set the language, spell-check will work when you click the spell-check button.
Note: I have the following spell-check dictionaries installed: Arabic, English, Spanish, French, Italian, Portuguese.
I am running Windows 8.1, so I don't know if this problem is on other OSs too.
I have attached a document ("LibreOffice Tweaks, Help, Tips, Tricks, & Notes - Gabriel - 20160116.pdf") detailing the process in paragraph 2. Note that there is also a second, lesser bug which makes "automatic spell checking" NOT retroactive to already-existing text. See the attachment, under the subparagraph 2.1.2 for more details.
There is quicker methods to find the solution, ask for help:
That said to define the language, the easy way is to modify the default cell style.
Don't forget to install appropriate dictionaries.
Note: current stable and supported versions are 4.4.7 and 5.0.4. Please upgrade to be sure to not run a version with known security bugs.
Closing as WorksForMe.
Best regards. JBF