How force Jenkins to show UI always in English?

Another way to achieve this:

Install the Locale plugin. You can set the default language for all users, no matter the language configured in their browser.

https://wiki.jenkins-ci.org/display/JENKINS/Locale+Plugin

It can be done in Chrome by setting default language in settings, and it's probably working on other browsers but I didn't test it.

1. Click Manage Jenkins > Manage Plugins > ['Available' tab]
2. In the Filter, search for: Locale .
3. Click on Locale Plugin checkbox and Install without restart button.

4. After installation is complete:

   • Under Manage Jenkins > Configure System there should be a "Locale" section.
   • Enter the default language_LOCALE code for English: en_US
   • Click on Ignore browser preference and force this language to all users checkbox.

You can use a Chrome plugin to change Request Headers on domain base (I'm using "Header Hacker" but I think there are many other plugins of that kind) and replace the "Accept-Language" header for your jenkins domain to "en-US,en;q=0.5".