You must specify the settings for supported languages in the SAP Gateway system. Settings include default and logon languages.
For more information, see the following documentation:
You have installed the same language packages for SAP Fiori in the SAP Gateway system and the back-end system.
Ensure that the default language of the SAP Gateway system is the same as the default language of the back-end system, for example, English. If this is not the case, ensure that the SAP Gateway system contains a subset of the languages of the back-end system.
The logon language for the ABAP application server is set according to the following process:
If the Mandatory Logon Data indicator has been activated for a service in transaction SICF, the system uses the language that was entered there.
If this is not the case, but the HTTP request contains the language in the HTTP header (as a header or a form field), you log on to the system using this language.
The browser settings of the calling client are then used. The system selects as the logon language the first language from the list that is maintained in the browser, and which is also installed in the SAP system. The language list is specified using the HTTP header field accept-language.
With Internet Explorer, you can for example set the language you require by choosing.
If no language is defined by this process, the classic SAP system mechanisms are used. The logon language is based on the user settings (in transaction SU01) and if nothing is entered here, the default language of the SAP system is used automatically.