This gets a little complicated so bear with me.

The installation has a locale selected - somewhere under Global Settings you should be able to set that. THEN each blog has a locale. Changing that should be under Blog settings ... somewhere ;) THEN each post has a locale. You can change that if you hit the expert tab when posting. Each will inherit from the previous if you don't change anything. So post gets it from blog gets it from installation.

The thing is if you change the Global Setting it won't automagically change the Blog setting for existing blogs, or the post setting for existing posts. That means you have to edit existing content to get the different locale for that blog or post.

Hope it helps!

My b2evolution Version: Not Entered

Not working.
How can I change the english texts? Where is the english language file? I'll translate it directly because any solution is not working. Two days spent so far. Not spent.... Lost !!! :(

Help please need a solution even thought if it means editing manually each line of the english language file !

There is no english language file. The core is written with translatable fields, and a locale is used to convert to the selected language (and other bits appropriate for the locale). You can see http://manual.b2evolution.net/Localization about making a new locale but first I would make sure your installation is translating to any other language.

Have you done all three things to making a post show a locale? Changed the installation locale, changed the blog locale, changed the post locale: all three matter but in truth once you change to (lets say) German then the translated bits will go to German. Once while talking with someone I changed his installation locale to German in order to show how translations worked is why I know that. We clicked off the page we were on and all sorts of bits in the back office went German. I had to sort of guess my way back to English ;)