I had the same problem in Word XP (Word 2002). Word was assuming that some of the text I typed was French. (In the status bar at the bottom, the language is displayed.) To prevent this, go to Tools | Language | Set Language | un-check Detect language automatically.
I guess you could install the French Autocorrections, but I do not want Word performing unnecessary actions, nor do I want it bloated with foreign language autocorrections.
This should prevent Word treating new text as French, but you may have text that Word has already determined to be French. To change all French text to another language:
To be safe, first save a back-up copy of your document in another file.
If track changes is on, you probably want to turn it off.
Go to the start of the document
Ctrl H (Replace)
In the "Find what" field type:
Click on More
Format | Language French (France)
Format: [specify the language you wish to use]