As far as I know, the "All languages" option applies to the custom dictionary only. Spellcheck as you type should work anyway.
Your friend could try using "Detect language automatically"; note, however, that it isn't 100% reliable, so creating a custom paragraph (or character) style with Spanish would be safer.
For more on spellcheck in general, see
http://wordfaqs.mvps.org/MasterSpellCheck.htm.