How start start Aras in German Language

Did you also increase the filesRevision counter in the web.config? If not, you can make a quick test by clearing your browser cache.

No, I did not increase the FilesRevision Counter . I tried changing the variable DefaultLocale and DefaultLanguage from English to German, then also I was not able to succeed.

But have you tried to clear your browser cache? The FileRevision counter is used to inform Clients that they shall reload the web elements. Otherwise, you will work with stuff from the cache, which may still be in english. 

Take a look at the web.config in folder Innovator/Client. The corresponding parameter is at the end:

<cachingModule moduleEnabled="true" filesRevision="3" />

But have you tried to clear your browser cache? The FileRevision counter is used to inform Clients that they shall reload the web elements. Otherwise, you will work with stuff from the cache, which may still be in english. 

Take a look at the web.config in folder Innovator/Client. The corresponding parameter is at the end:

<cachingModule moduleEnabled="true" filesRevision="3" />

Yes, I tried clearing the cache also.

It worked only after I changed the browser language to German.

Ah ok. I can confirm that ootb language is selected automatically accoring your client settings. 

If you want to select the language manually, you could try the concept described in this blog article:

https://cylnote.blogspot.com/2019/02/add-locale-options-to-login-page-of.html