Thanks for providing the link.
As far as I understand you need to replace the icons for the English version within Ninja Simple Icon Menu.
I see it's not actually needed to translate words, because there are only icons (custom images) displayed without the icon's text (which is optional in the module).
Maybe this is were it goes wrong.
Because you can't change the actual icons for the English version.
I've no solid clue because I'm not up to date as it comes to JoomFish because I don't use it myself or have tested it with Ninja Simple Icon Menu.
What I can suggest is that you create two modules, one for your native language and one for the English language. Just upload your custom icons/images (both native and English) in the same folder that Ninja Simple Icon Menu uses.
Then in the settings within JoomFish, try to assign each module to it's belonging language.
I'm not sure if this will work or if it's even possible, but it's the only suggestion I have at the moment.
I hope this helps.
Let us know how it goes.