If the Firefox user interface (menu bar) is in the wrong language or if you want to change the current language then you can get Firefox in the language of your choice here:

• Firefox 5.0.x: http://www.mozilla.com/en-US/firefox/all.html

thanks but is not there any way to Cheng that without new download ?

You can install the en-US language pack from:

• http://releases.mozilla.org/pub/mozilla.org/firefox/releases/latest/win32/xpi/

You can set the value of the pref "general.useragent.locale" on the about:config page to language code of the version that you have downloaded (e.g. "en-US" or "en-GB").

See also:

• http://kb.mozillazine.org/Language_packs

To open the about:config page, type about:config in the location (address) bar and press the "Enter" key, just like you type the url of a website to open a website.
If you see a warning then you can confirm that you want to access that page.
You can use the Filter bar at to top of the about:config page to locate a pref more easily.