Always use English in WCM edit mode

Our platform is used by English speaking content authors to author content in all languages.

We wish to force the WCM authoring interface to use English for all out-of-the-box strings (editbars, context menus, sidekick, etc), while still using the i18n bundle for our own strings.

So far:

•  Tried setting the user's (and group's) preferences > language to English; WCM was still localized, even after re-logging in.  Even if it worked, I imagine it would use English for our own localized strings, which is not acceptable.
•  Considered implementing RequestLocaleResolver to set the locale to 'en' for all author requests in WCM edit mode.  Again, I imagine it would use English for our own localized strings, which is not acceptable.
•  Considered overlaying the WCM i18n dictionary, /libs/wcm/core/i18n.  I doubt this will work unless we overlay each of the i18n files with all of the English strings.  Less than desirable.
•  Same as the overlay approach, but instead adding a new i18n dictionary under /apps/myProject/, again including all English strings as "translations" in the other languages.  And again, less than desirable.
•  Considered removing the WCM i18n dictionary, /libs/wcm/core/i18n.  This is, of course, discouraged.

​What is the best approach to this?