Scenario: Let's say you have an English CHM file and you want to have a link to a French version of the CHM file, here is how you would achieve that.
Firstly, both CHM files should be in the same folder as CHM file you are using. If they are not then the path specified needs to be the full path, and this is rarely known because the user could move the files etc.
Highlight the link text, i.e. “Click here to open the French help file”
Press F4 to open the Link Editor
Set the “Type of Link” to “Internet”
Set the url to the chm name and optionally a page within the chm file as follows: its:Fast-Help-FR.chm::\ApplicationSupport.html
That would open the ApplicationSupport page within the French Fast-Help-FR.chm file.