Foreign words and names

Brodeur being a family name on one side of my family, I wanted to ask how would you go about transliterating a name from outside of Old Norse? And if the name ends in a way that a Norse word wouldn't, how would it change case?

--- In norse_course@yahoogroups.com, "Patricia W" <originalpatricia@...> wrote:
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> I found this - it does also concern Garm !!
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> Hope this comes through ok
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> Then shall the dog Garmr be loosed, which is bound before Gnipa's Cave: he is the greatest monster; he shall do battle with Týr, and each become the other's slayer. - Brodeur's translation