Go to your config page by adding the parameter lang=yourlanguage, e.g.
http://yoursite.tld/your_coppermine_folder/admin.php?lang=yourlanguageAn example for the demo page would be
http://coppermine-gallery.net/demo/cpg14x/admin.php?lang=dutch - this would set the field to "dutch".
However, you have to understand how coppermine's language system works - here's an excerpt of the docs of the devel branch that apply to cpg1.4.x as well:
Language
This sets the default language for your gallery. All language files are stored in the lang directory on your server.
Languages and internationalization (often refered to as i18n) is a complicated and complex thing. You (as Coppermine admin) probably don't want to go into details, so this documentation skips the in-depth issues existing with i18n and just gives you an overview how Coppermine handles languages:
By default, language files are unicode encoded files. If you set "Character encoding" to "Unicode (utf-8)" then the script will auto detect the preferred language of your visitors based on what default language is configured in their browsers. If the corresponding language is available in your language directory, it will be used. Otherwise, the default language file will be used.
When the script auto detects the preferred language, it stores the result in a cookie on the visitor's computer. To reset this cookie (and thus force the script to do another auto detection) the user must call this autodetect function with something like: http://yoursite.com/coppermine_dir/index.php?lang=xxx
These steps are performed by the script:
* Step one: Check "has a specific language been set by cookie or URL parameter?". If yes, the gallery will be displayed in that language, all subsequent steps are being skipped
* Step two: which language has the user set as default language in his browser? If that language exists as Coppermine language file, it will be used - the subsequent step will be skipped.
* Last step: only if the previous steps both don't apply, the default language that the admin has set up on the config page will be taken into account
If my explanation doesn't work for you, post a link to your coppermine-driven gallery.