I'm afraid translate() doesn't work like that. Translate replaces single characters with other single characters, or it can remove single characters:
http://www.w3.org/TR/xpath/#function-translate
You can probably rig up something with rules and tricky XPath functions, but you risk causing an infinite loop error if there are a lot of double semicolons. The other alternative is to use code which, can remove them pretty easily.
Can I ask why your values have these double semicolons in them to begin with?