As you already noticed, D365fO works with URL query parameters.
One example usage is to open a menuitem directly by using &mi=MenuitemName:

https://usnconeboxax1aos.cloud.onebox.dynamics.com/?cmp=DEMF&mi=CustParameters

When you are working with different languages on the client, there is a way to change the language faster than changing user specific options.
Just use the query parameter &lng=LANG in the URL:

https://usnconeboxax1aos.cloud.onebox.dynamics.com/?cmp=DEMF&mi=CustParameters&lng=en-us

This will change the client language to the specified language as long as the query parameter is attached to the url.