Language selector vertical instead horizontal

Hello Everybody!

I don’t know why, I’m unable to put my language selector bar on horizontal.
I think I have try almost all class and id possibilities… My knowledge seems too bad…
Is there anybody here that can help me?
You can see the problem here: https://imagiweb.ch/ruedi/de/

Thanks in advance for your help!

BR,
Etienne

https://ww.wp.xz.cn/plugins/polylang/