May be Outlook is buggy, but your mentioned Thunderbird has it's own issue:
When I want to use german names for a user I setup his mail account with a folder named "Papierkorb" as trash folder (german translation). This can be used with many email clients without problems. But a german Thunderbird wants to create a new folder "Trash" and displays it as "Papierkorb". So what is the result? In Thunderbird I have two folders named as "Papierkorb" where I see in other clients a folder "Trash" and a folder "Papierkorb". (The same applies to sent, draft and templates folders.)
It's 'simply' a translation issue and one of the problems with translating folder names. The same happens with roundcube, and I removed the folder translation code from the source. It's just too confusing for people when they end up with 2 folders that seem to have the same name.
Cor