Hi Mike,
I can't explain the difference between Chrome and IE. It doesn't make sense to me either.
In BI launchpad or CMC, what are the PVL and Locale settings for your user account? (Preferences link along the top toolbar)? Ensure they are both EN
Also, what version of BI4.1 are you using? I'm fairly sure you can add Language packs without a full re-install. I can't remember exactly when, but I believe it was SP5. Just run the setup from add/remove programs and select "Modify".
Dan