Not exactly what you're looking for, but in Esperanto the words for right and left are "Dekstre" and "Maldekstre" which roughly translates to something"right" and "anti-right" so while the first letter is different they both have the same root word, which is something I don't think a lot of languages do in this case.

As far as labeling headphones and such, it's not really an issue since I don't think anyone is making products with Esperantists in mind.