Hi, I don't find how to change the language of the admin panel.

In Option \ General, I choosed "French" in language, but, my admin panel is always in english.

Many thanks

Your server probably does not support other languages.

You can check if the [i]Locale setting[/i] has failed in the [i]Installation information[/i] on the Admin -> Overview tab.

Is the Overview tab, I got :

Current locale setting: fr_FR.UTF8

So I think french is supported.

I see, but which languages are checked and which plugins are activated?

Under Options –> General, you may have, for example, the radio button checked vis-à-vis French, but checkmarks vis-à-vis English, French and Spanish.
Let's also suppose that the "Multilingual" checkbox is NOT checked.

Then, what happens, is that your custom strings, such as gallery, album and image description will be in only one language, which will be defined as "French". However, Zenphoto menus and dialogues, including those from multilingual themes, will be available in English, French and Spanish. So who decides which language you will see?
– if a user is registered, then the language displayed is the one chosen in the User data (admin/User panel);
– if a user is unregistered, I think the language is chosen amongst those available languages according to the browser's language preferences;
– if the dynamic-locale extension is active, then the user may override the default selection.

Michael has got it correct. In addition in the 1.4.3 release the language can be set by the adding a language designator as a subdomain in the URI. e.g. es.mydomain.com will select Spanish. Of course your server subdomain handling will have to suport this.