Static labels used in the WebHelp output are kept in translation files in the DITA-OT/xsl/common folder. This folder is found either in the Oxygen XML Author plugin installation folder, or elsewhere if you are using a different DITA-OT distribution. Translation files have the strings-lang1-lang2.xml name format, where lang1 and lang2 are ISO language codes. For example, the US English text is kept in the strings-en-us.xml file.
Follow these steps to localize the interface of the WebHelp output (for simplicity sake, let us suppose you want to localize the WebHelp interface into Canadian French.):