Language is a character/font level formatting attribute, although it's set
using Tools - Language, rather than Format - Font. I.e., you can select any
amount of text, and choose Tools - Language - Set Language, and format the
selected text as any language. If you have the corresponding proofing tools
installed on your computer, then you can perform spelling and grammar
checking in that language. For example, I frequently work in Spanish and
English. By default, my installation of Office assumes everything will be
English US.
That said... if yours is set to English Can, you very likely do have the
correct proofing tools. So, it's probably a settings issue of some kind.
Let me ask this... do grammar & spelling tools work otherwise? I.e., if you
make deliberate spelling/grammar mistakes, does Word find them?
Note: if the problem is a settings issue, it's very unlikely that removing &
reinstalling will solve the issue, since removing/reinstalling, by design,
leave many Office settings unchanged.