I have noticed that using Finnish has become increasingly popular in the
'chat'-channel. I know, it states in the helpfiles that only the game-related
public channels (bat, wanted, sales, newbie...) are English-only. But isn't
there a very own channel for Finnish chatting? I'm proposing that Chat would
be made English-only and if someone wants to chat in Finnish, (s)he can use
the Finnish channel.

im not even fin but i'll rate this -1 its chat channel, if they want to
chat in fin they can..end of story

But there exits a channel for Finnish chatting, why won't they use it?

possibly because more people have chat on, or just because they want to use
chat..nothing stops us from using english on fin channels..i have a few times.
now i will stop spamming news, goodday