Luxembourgish.
People: Luxembourgers, Adjective: Luxembourgians
Both Luxembourgish and Luxembourgen are found in English dictionaries.
An adjective for someone who is rich could be wealthy.
'Friendly' is an adjective because you'd use it to describe someone. Any word that can be used to describe someone (a noun) is an adjective.
It is an adjective clause as in "(someone) who can cook."
Yes you can use it as an adjective by saying someone is 'arachnophobic'
The capital of Luxembourg is called Luxembourg. It is also known as Luxembourg City.
The word lonely is an adjective. It describes someone who is unhappy at being alone.
Luxembourg, the capital of Luxembourg is located at the southern part of Luxembourg.
buy them a plan ticket and take them to Luxembourg
The word wily is an adjective. It is used to describe someone who is cunning.
The proper adjective for someone or something from Guyana is Guyanese.