Variations may include:
Dubet, Dube, Dubée, Dubais, Dubaie, Dubey, Dubay, Dubbée, Dubbee, Dubbaie, Dubber, Dubbey, Dubbay, etc.
These answers were borrowed from: http://www.houseofnames.com/dube-family-crest and http://www.houseofnames.com/fc.asp?s=dub%E9 You might also try looking up the variations on House of Names to see where that leads you. I have thought of a few other variations including:
Dubie, Dubbie, Dubbais, Dubbaie, Dubbet, Dubbe, Dubbeh, Dubeh, Doobay, Doobee, Doobie, Doobeh, Doobé, Doobée...
There are MANY possibilities. Your best chance of figuring out this mystery is using a soundex or sounding out possibilities. You could also try looking up the Germanic spelling by finding out which sounds combined which sound like Dubé...
Another possibility is that the last name was given by occupation. Dubé refers to a brewer in French, so you may wish to look up variations of the surname Brewer as well (http://www.houseofnames.com/brewer-history/German). The last name Brewer is of Germanic origin. You must remember that scribes often recorded names as they sounded or as they thought the names should be... They lacked spelling rules in medieval times. They also may not have been able to speak the languages of the immigrants, so surnames may have been recorded by observing the person. If they were brewing something, their last name became Brewer. Illiterate people also would have no idea how to spell or write their names to help the scribe... This is why we often see people signing an "X" rather than their name on documents when tracing the roots of our family.
Another important factor to remember is that the borders of European countries have been redrawn frequently through history. What your ancestors referred to as Germany may no longer be Germany, or those who told you the stories may be referring to modern day Germany rather than the country it was in the past. Maybe they were just referring to a country which spoke a Germanic language... Your best bet would be to try to find a specific place name (like a city) that your ancestors lived nearby. You will then be able to look at old maps and investigate which country the city was in at any given time... That will help you to decide where you will continue your exciting search. Best of luck!