English version of my site show french strings [closed]

If these theme strings are prepared for translation and the theme is not in english by default (they’re outputed with __() or _e() functions) and you include your theme textdomain correctly, then you probably haven’t translated these strings to english.

WPML had/has some tool to do this, but it isn’t very user-friendly (at least I don’t like this tool). I’d suggest using Codestyling Localization plugin.

Install it, rescan your theme directory (it will find all translation strings) and then add missing translations. Don’t forget to build .mo files after translating strings (without it new translations won’t work).

EDIT:
It occured that it was some problem with .po/.mo files. Installing Codestyling Localization and rebuilding translation files solved this problem.