Ah, I had the same question!
I'll be interested in knowing what Blindmime was wanting to do, but in my own case:
I wanted to add a link for "Blogs" to my top navigation menu strip.
To do so, I copied and edited one that was already there in my skin's header_menu/tpl template, like for "videos" and changed the code to point the new link to the /blog page. But the code had an "ID #" which would need to be the line number for the word "Blogs" in the Language file...only there was no word Blogs in that language file. If I could add it, then I could fill in the line ID# in the code to create the link, and all my header menu link codes would be similarly constructed.
I stumbled onto a workaround for it (which I won't describe), but I still was left wondering how I could add a word or term to a module's language file so i could insert the line# ID for that word in code when needed. Yikes hope this isn't too confusing. Maybe I am missing some key concept about language strings/files and how they are used or created.
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...just another satisfied Jamroom customer.
Migrated from Ning to Jamroom June 2015
updated by @strumelia: 12/13/14 09:19:13AM