I've resolved this issue. I'm new to MODx, so the README wasn't quite detailed enough in how to set this up - I think I'm still getting used to the MODx terminology.
So, just to be a little more explicit in the setup documentation for newbies like me :
From here :
http://rtfm.modx.com/extras/revo/lingua
the key to the set up is here :
http://rtfm.modx.com/download/attachments/3c7aceb2105f8370062ab6139e964a8a/lingua_context_settings.png
Go to the Context page :
/manager/?a=context
right click the row that says 'web' --> Update Context
Click 'Create New'
Key : modrequest.class
FieldType : Textfield
Name : Request Handler Class
Namespace : Core
Description : setting_modRequest.class_desc
Value : LinguaRequest
Once you save this setting, edit your Home page resource and enter content for English, then toggle to French and enter content.
You will then be able to see your output by passing in the lang paramters into the URL :
/index.php?id=1&lang=fr
/index.php?id=1&lang=en
HTH, dave
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