How to change user's language (locale) back to English? [duplicate]
Solution 1:
Specify the language at the login prompt after selecting the user. When asked whether to make the selection the new default, select yes.
Solution 2:
The per-user locale default for the Desktop session is stored in ~/.dmrc. This is the file that is updated when selecting a new locale at the GDM screen. GDM uses this to set up the environment when starting the user's session.