I noticed that I could not disable “Detect language automatically” in Word. Even though the option was disabled, word still insisted on changing the language for the text I was writing. I would change it back to whatever language I was using, but then suddenly, Word would revert back to the other language.
It turned out that one of my header “styles” was set to that language and that every time I used that particular header style, the language changed. So it wasn’t the “Detect language automatically” that didn’t work, I was the header style that actually did work though It wasn’t intentional.
To check the language of a style , simply right click the style (on top of the page) and select “Modify”. Then click the button on the bottom left that says “Style”. Select “language” from the drop-down menu. In the pop-up window you see what language the style is set to. Change it to whatever you need it to be, and click ok.
You might have to check the other styles too, to find which one is changing. You can also see it change on the bottom of the document, when applying styles. Try them out one by one, and see which one changes the language.