We recently did an upgrade of our SAP LOGON into Version 730.
Suddenly my default logon language was no longer EN, but NL instead. Although I am Dutch speaking I usually work in English while doing customizing and other stuff, so rather annoying.
I quickly checked what influences the logon language and found following aspects:
1) System Parameter zcsa/system_language which can be checked using transaction code RZ11
This was set to default E (English). So this was not the problem.
2) I also checked my logon language in my User Master Record via transaction code SU3. This was set to NL, and I changed it into EN.
I still had default logon language set to NL when logging on again.
3) I also checked and changed the logon language in my SAP Logon Option settings into EN:
After having made this change, my default logon language was set back to EN.