Hi khneal,
everything is completely on English. Regarding the underlying host system: system is running on English, and browser is also running on English. Nevertheless, some words are localized to German, e.g. "Dashboard" to "Übersicht". What I've done now for a quick fix is to install the Locale plugin and again set the locale to en_EN, and now also Blue Ocean is completely running against English. This looks like a workaround though since Blue Ocean should already automatically align with default settings.
michaelhuettermann if you are in regular jenkins - do you see german translations there? how do you switch the language with it normally?