This is just a demo: in phpBB3 forums you can use any language, the only problem is whether you have a font supporting these characters. The problem with the absense of required keyboard driver can be solved with Virtual Keyboard

Lakhota: Aŋpétu léčhečaka čha él matʼíŋ kta huŋšé.
Russian: Здравствуйте, дорогие товарищи!
Korean: 안녕하십니까
Chinese: 您好馬?