I haven’t worked with the Randomtext plugin, so I just installed it on a test site.
I had a look at the code and the plugin has not been internationalised whatsoever.
It generates its own category (Installer), instead of grabbing one of your existing categories. There doesn’t seem to be a way to translate this default category and even when adding a new category, it also is not possible to translate.
The cause of this is most likely due to the fact that the plugin creates its own table in the database (prefix_randomtext) and this table communicates only with the plugin and nothing else.
I would say that unless this plugin is completely recoded it is fully incompatible with WPML.