: Then how did the Germans speak it as a common language in
: Northern Europe and the Romans have knowledge of it?
: After all, Gζlic has an uncany resemlance to Gallic.
The Germans--Goths at the time--did not speak Gaelic, nor Gaulish, but rather Gothic. The Celtic languages are not Germanic. And the Romans encountered virtually all Celtic tongues--they occupied Western Europe, after all, and also England and Scotland during the time when both the Scotii and the Picts were in residence.
http://w1.xrefer.com/entry.jsp?xrefid=441440
gives a brief overview of Celtic languages
and
http://softrat.home.mindspring.com/germanic.html
gives a nice tree of the Germanic ones. And if you're not sick of the subject after that, try
http://www.krysstal.com/langfams.html
--SiliconDream (Yay! An excuse to use an image!)